Lots of fun input! Yeah, markers certainly qualify, as do paints (all sorts). LOL on the black, Melissa. I load mostly with black. Brown is my runner-up followed by blue. Once in a huge while I'll load with red, green, etc. And I should note that most of the stamps I'm using are 'detail' ones rather than 'solids'.
With the solids, I more apt to load with other colors--unless I'm going for a silhouette look.
OK. Now for the meat & taters question... When coloring in a stamped images, how many colors do you NEED?
Like most of us, I 'need' every color, but I find that I don't need all the colors to be inks-only. That said, I certainly have a good range of different colored inks--especially Distress & StazOn ones. Plus several just dye inks--most of which I've had for years. Markers are another way for me to get the most diversity for my $ And (like crayons), I can use them to 'make' colors. By layering & blending, I can start with one color & make a deeper version by swiping it with another marker or crayon. Crayons work really well with this. And by layering white on a base color, I can lighten as well as darken.
Once in awhile, I use (liquid) paint to color in a stamped image.