photoshop is $$$
you can also do this with ImageJ (from cuturl('http://rsb.info.nih.gov/ij/') ), a free software from NIH
1. "open" two/three gray images in ImageJ (or open RGB images, which are represent different channels, and convert to 8-bit by "Image -> Type -> 8bit")
2. use "Process -> Enhance Contrast" to get maximal visual effect
3. use "Image -> Color -> RGB Merge" to get your figure ~~
btw, ImageJ also can do deconvolution, but you need use the scope to get the psm file