The Commandos series was good, though 3 was disappointingly short and Strike Force was dodgy, though not dreadful. Despite being seen as a total ripoff of the series, I thought the first Desperados was great, and it's a shame the second one turned out to be a bit of a mess. Haven't bothered to try and find the new one anywhere.
On the subject of chameleon games, there was an Atari ST platformer/puzzler called Colour Clash. Best bit of the game was the support shareware screen that had pigs sliding down a slope and a crocodile waiting to catch them in its mouth, but the game itself was pretty good too. There was a PC remake
made a while ago, no pigs and crocodile bit but otherwise mostly intact. Colour changing just changes abilities though, no stealth purpose to it, so count me amongst those who'd like to see that.