I have an suggestion for an added feature to Photoshop. It would be a Selective Colour Change Brush. Much like the current Colour Replacement Tool, but with the added ability to only change the colour of the colour you first click on. Much like how the Background Eraser Tool erases the colour you first click on, this feature would change the colour to your preferred colour, instead of removing it.
This could also be expaned to have a colour selection brush. Often, I find that I need to select a certain colour, and only in a defined range of the image I am working on. Rather than use the Colour Selection feature, as it is, and then have to delselect the rest, it would be handy to be able to just use a brush like tool. You'd click on the colour in the area you're focusing on, hold the mouse button down, and then move the brush around to select only that particular colour.
For the type of work I do, features like these would save me a bunch of time.