Any enlarger can do both B&W and color. The question is how easily the enlarger can handle different types of filtration. Variable contrast (VC) B&W papers are sensitive to blue and green light and produce different contrast depending on the amount of blue and green light they receive. Thus, yellow (anti-blue) and magenta (anti-green) filters are used to block blue and green light, respectively. Color paper is sensitive to red, green, and blue light, so color enlargers use cyan (anti-red), magenta, and yellow filters to control the amount of each type of light that hits the paper, thus affecting color balance. (In practice, cyan filters are seldom necessary for color printing.)
Enlargers intended for color printing typically have cyan, magenta, and yellow filters built in. (A few models use red, green, and blue light sources instead of filters.) B&W enlargers typically either have no built-in filters or have just magenta and yellow filters (or separate blue and green lights). Most B&W enlargers, except for very old models, have filter drawers into which you can place filters of any color you like. You can get color filter sets to use with such enlargers, to use them for color printing; however, most people prefer true color enlargers, since adjusting a dial is easier than juggling filters in a filter drawer. Even if an enlarger has no filter drawer, you can use under-lens filters, although these can theoretically degrade the image quality more than in-enlarger filters.
There are also differences between condenser vs. diffusion enlargers, enlargers capable of handling different negative sizes, etc. As you're new to this I wouldn't worry too much about the details. Get something that handles the negative formats you use (and perhaps a bit bigger -- for instance, 6x6 if you do 35mm) and that has whatever built-in filters you want. If you later discover you need something more or different, then given the current marketplace, upgrading won't cost you that much.
FWIW, I posted this message about a free enlarger in the San Francisco area. I've no idea if you're even on the same continent as the person who's giving away that enlarger, but if you happen to be in that area, it's hard to go wrong with a price of $0!