Colonial troops made up of native soldiers were very important in both world wars, and often hoped their service would help further causes of independence.
Once these countries were gaining independence, were soldiers in those units (Kings African Rifles, Senegalese Tirailleurs, French Army of Africa) expected to hand over their equipment? Were any that wished to move to the colonizing nation given permission to? Were these soldiers ever incriminated for suppressing their own nations independence movements in the past?
I will only talk about French colonial troops, which is already a large chunk of history.
French Colonial troops can be roughly divided into three groups:
Regular troops made (mostly) of European recruits, who could be French people from continental France, French colonists, or foreigners. The Foreign Legion is the best known of these units, but other colonial "European" troops included the Bataillons d'infanterie légère d'Afrique (aka Bat'Af), which used to be disciplinary units, and the Zouaves, which started as native Algerian units but soon became mostly European.
Regular troops made of native recruits from the Colonies with French officers (and native low-ranking officers). Examples: the Tirailleurs Sénégalais/Algériens/Indochinois. The oldest colonial troops had started as auxiliaries: the first African tirailleurs had been former slaves or prisoners, while in North Africa and Indochina entire clans/tribes/ethnic minorities, had rallied the French. By the end of the century, these auxiliaries had been progressively organised in structured units and, in 1900, there were integrated either in the Armée d'Afrique (for North African units) or in the Armée Coloniale (for African and Indochinese units).
Auxiliary troops (supplétifs) made of native recruits from the Colonies, and created, sometimes temporarily, for ad hoc military goals. While some auxiliary units had become regular units, many new ones were massively recruited during the Indochina and Algeria wars. The status of these men was highly variable, but it was generally more flexible and precarious than that of regular troops. Auxiliaries were generally less trusted than regular troops and used in non-offensive capabilities (as guards or for policing activities for instance) but some, such as the commando units recruited in Indochinese ethnic minorities, did fight in military operations.
Native colonial troops were created for several reasons.
Colonial troops were used in the Colonies, both for conquest and to fight insurgencies, and as well as in European wars, and sometimes for policing operations in France. North African troops, notably, fought in most of the wars where France was involved: Crimea, Franco-Prussian war of 1870, WW1, Rif war, WW2, Indochina, Algeria...
The fate of colonial units from 1945 to the independence of each country varied widely. In most cases, the units were simply dissolved when they were no longer deemed useful. Some "European" units were repatriated or sent to other overseas territories. The units of the Chasseurs d'Afrique, for instance, who were mostly European, were all dissolved (most of them in 1962-1964) except 3 that are still active today. Some native units (notably some Senegalese Tirailleurs) were renamed and repatriated in France (I'm not sure about their soldiers, but some Africans were French citizens). There was also the strange case of the 5th Regiment of Moroccan Tirailleurs, who remained (with its own military brothel...) in Dijon (France) until 1965, 9 years after the independence of Morocco.
The fate of the individual soldiers eventually depended on the political situation. When their country's independence happened peacefully, as was the case in subsaharan Africa and to some extent in the protectorates of Morocco and Tunisia, they were generally able to go home (or to France) and either become civilians or join the new national armies. In Algeria, the fate of the native soldiers, and notably of the auxiliaries, the harkis, was more tragic.
Here are some short descriptions of specific situations.
The Tirailleurs Sénégalais after WW2
These units, despite their name, included soldiers from all over French (subsaharan) Africa, not just Sénégal. After the defeat of 1940, many tirailleurs who had fought in France were discharged and sent home by the Vichy government, eager to get rid of them. Even though colonial propaganda praised these men, they were treated badly when it came to discharge and repatriate them, and they were subjected to discriminations regarding pay, bonuses, and living conditions. Late 1944, a group of about 1300 repatriated POW from the tirailleurs, who had been placed in a holding camp in Thiaroye, near Dakar, protested the failure of the authorities to pay salary arrears, discharge allowances and other bonuses that had been promised to them. Their "mutiny" was repressed in a bloody fashion, causing officially 35 deaths among the tirailleurs.
The personal situation of the repatriated tirailleurs was variable. Many have been away from home for years, even decades, and had trouble finding jobs and readaptating to the world of rural Africa. However, they brought new knowledge from the outside world: some became agents of change and former tirailleurs participated in the independence movements. Léopold Sédar Senghor was one of them, though he had been of course politically active before the war. Other tirailleurs continued to serve in France's post WW2 colonial wars, first in Madagascar, then in Indochina and later in Algeria.
After the independence, many former soldiers of the French African colonies joined the new national armies, something that France saw in a positive light. Future strongmen Moussa Traoré (Mali), Jean-Bedel Bokassa (Centrafrican Republic) and Mathieu Kérékou (Bénin) started their military careers in the French army, where they were trained as officers, before joining their respective national armies in the 1960s and eventually getting in power by less than democratic means.
African veterans of the French army saw their military pensions "frozen" in 1959 - ie the amount they received remained unchanged over the years, unlike that of French veterans. This was a (small) thorn in the side of French-African relations, and it took 50 years to fix: in 2010, President Sarkozy "unfroze" the pensions, which by then still concerned 10,000 veterans and 20,000 heirs of veterans.
Franco-Vietnamese troops after 1954
At the beginning of the Indochina war in 1946, the Expeditionary Corps included at first 100,000 men, including 31,000 native (regular) soldiers. In addition, there were thousands of partisans and auxiliaries. When the official army of the pro-French State of Vietnam was created in 1949, some native troops, regular and auxiliaries, were transfered to the new army, while other remained in the French army. After the French defeat at Dien Bien Phu, thousands of these men and their families were evacuated in the South. Others defected to the Viet Minh or were executed as traitors. A handful of naturalized Vietnamese and mixed-race people resettled in France, where they were kept in camps for several years.
In South Vietnam, former Vietnamese soldiers of the French army or of the State of Vietnam joined the national army of the new Republic. In December 1955, in a display of nationalism that infuriated French authorities, several officers, notably general Trần Văn Đôn, Diệm's chief of staff and a French citizen by birth, organized a ceremony in Saigon in which the French-style military rank insignias were burnt and replaced with American-style new ones.
Morocco in 1956
The Army of Liberation merged many of its units with former French colonial troops, resulting in a new army dominated by colonial soldiers, such as Ben Hammou Kettani (who had been a general in the French army), Mohammed Ben Mizian (his equivalent in the Spanish army), and Major Mohammed Oufkir (also a former officer in the French army). The police force was similarly formed from the old colonial police
-> to be continued