The extra numbers (not letters, numbers) on the model number are the color. So, for example, cotton white would be listed as CST744S#01 or CST744S-01. 01 is cotton white, 03 is bone, 11 is colonial white, 12 is sedona beige, and 51 is ebony(black). When you look in a Toto tank, you will usually see the color stamped in it in big numerals by themselves, separate from the tank model number, like this: #01
I would hesitate to give advice about matching Mansfield colors. However, if you have the color letter or number in your mansfield tank, post it here and maybe we can find a comparison chart or someone will know.
Additional letters in the model number mean additional things. CST744SG is with sanagloss. CST744SL is in ADA height. Other letters cover such things as a right-hand flush lever, bolt-down lid, or insulated tank, none of which you are likely to want or need.
I would point out that the CST744E is a 1.28gpf version of the same toilet, which might qualify for a watersense rebate in your jurisdiction. It flushes almost as well as the 1.6gpf version in most circumstances. You can check the list of jurisdictions that offer such rebates at the following link, but be sure to validate the information to make sure the program is still in effect in that jursidction: http://www.epa.gov/WaterSense/rebate...ney_water.html
Regardless, you are buying a great toilet, of which I have two, which we love.