You could argue that Denmark did that with the Faeroes, Greenland and maybe also Iceland, depending on whether you count it as being colonial. In the 1953 constitution the Faeroes and Greenland were incorporated into Denmark as "amts" (An old Danish administrative division just above the municipality) and both gained two seats in the main electoral body, Folketinget. The Faeroes weren't technically classified as colonial before this but still had no representation but Greenland was classified as a colonial holding at the time and so switched status to being a fully incorporated territory. In doing so citizens of both countries also became full Danish citizens on paper but there was still a lot of discrimination and specifically Greenlanders faced a lot of racism. Because this would also mark the start of a project of cultural destruction in Greenland that sought to impose a Danish style of government and economy upon the native inhabitants, all justified as an altruistic program. In the new government bureaucracy and companies white Danes were often clearly favored and privileged with better jobs and pay. This is generally seen as the cause of Greenland's high rate of alcoholism and suicide.

The main hangup here is whether or not Denmark can really be counted as a colonial power at this point. After the Napoleonic Wars what used to be Denmark-Norway fell from it's status as a great power and stopped being an active participant in the colonial game. Therefore the colonial holdings of Denmark were basically the left-overs of that period and Denmark was not part of the colonial game and basically only got to hang on to the stuff no one else wanted, or the stuff that didn't break away themselves. As a result Denmark was not really operating Greenland as a colony in the same way actual colonial empires like the UK, France, Germany, Japan, US and so on did, with a focus on resource extraction and sale of industrial goods from the mainland all maintained by a large military occupation. Denmark was, as Iceland had shown, incapable of actually resisting any kind of independence movement if they were serious enough and had actually been trying to get rid of it's former colonies for the last 100 years, Greenland had almost been sold itself. In fact Denmark could barely even maintain it's claim to Greenland, almost losing about a third of it to Norway at one point because Denmark had no active presence in the area.

The other hangup is that of course this happened as the colonial age was already ending, so it can easily be seen as a very naked attempt to try to maintain control of the colony and get ahead of a budding independence movement. That was very clearly what happened in the Faeroes.