If slides will be all you scan, you might be better off with a pure slide scanner. There are three things to look for in a color scanner. First is color depth, which is measured in bits per pixel. Higher bit depths allow for more accurate color reproduction of scanned images. Second, look for the resolution of the scanner.
Resolution is measured by how many dots per inch, dpi, a scan captures.
If the bulk of your work consists of graphics and manipulating images, at least 600x600 true resolution is required for decent detail capture. Discount sales pitches that talk about a scanner's interpolated resolution. It is a way to create additional pixels that has not been captured in the original scan, which can be helpful when enlarging scans but does not improve upon the detail captured. Finally, test for scan speed. Unfortunately, the only reliable way to get a sense of how fast a unit scans is to try some samples.