Well, you take ONE regular chao (what you were given the first time you ever entered the chao garden) and ONE colored chao (like blue or red it doesn't matter, whatever you want it to be close to) of your choice... Yes- they both need to be adult duh...
So then we make them mate, buy a heart fruit from the black market if they both don't already have a flower circle around them (Although sometimes only one chao with the flower circle is needed)
Now if they're both ready: you MUST save and exit before you mate them at all! Remember, you might end up hatching a baby that looks like just another copy of it's parents (Like a regular or the simple color)
They will make their egg, hatch it
without wasting time. Just f***ing throw the egg at the wall, come on,
trust me you don't always have much luck getting a two-tone right away
it could take a lot of frustrating tries.
If it turns out as plain, then reset your game, reenter, and retry until you get a baby chao:
What you're looking for is a chao with the base color of the colored parent, but look closely at it's hands and feet- you should see a different tinge to them- perhaps darker or lighter.
Some of the colors are difficult to notice, what I always do is pet them with a dark character to see if the color stands out more from the black, you'll know it when you see it.
Anyway, these chao are amazing, especially after their first evolution, their colors are very exiting and dramatic. You can do it with all the basic colors which you can buy at the black market. You can't make jewel two-toned chao.
To mix it up, use a shiny chao as a parent, try making a shiny two-tone. Use your imagination once in a while hehe.