I know that the colonized cultures were second class citizens (or worse), but were White British people held accountable at all for crimes against them?
Any examples from the 19th century British colonies would be especially appreciated.
In India, not really.
You see, most murders of Indians by whites were classified as a "burst spleen". It was a very nice circle of complicity.
The offender was white, the local police superintendent was white, the doctor was white, the judge was white.
So the doctor would explain to the judge that the dead Indian had a swollen spleen and when the white person had hit him, the spleen had burst. The death was therefore accidental. This was particularly endemic in the tea gardens where the poor, illiterate tribal labourers were victims of horrific abuse.
Then there were the incidents of Indians accidentally getting shot during hunts. The British would always claim that they thought they were shooting at animals.
An excellent book on this topic is
Colonial Justice in British India: White Violence and the Rule of Law (Cambridge Studies in Indian History and Society) by Elizabeth Kolsky (CUP 2011)