Well, I may not be much of an artist, but I've 
been having the same difficulties getting a 
decent, set flesh tone, and here's what I've 
muddled through so far. It might help.

First off, the "radiants" from Cartoon Colour 
were made for "highlights" and "special effects" 
(I believe that's how they put it on the site) 
and are suppose to be vividly bright. I have the 
blue and yellow, and they are LOUD! The yellow is 
neon and hard as heck to mix into something more 
tame. =P 

But if you buy the plain ole' orange and mix with 
white, you should be able to get a good enough 
skin color. They also have a color specifically 
called "flesh". That might be better (haven't 
tried it yet).

Actually, what I found to work best when dealing 
with the vinyl paints is mixing brown or light 
brown with a lot of white. It's not as bold as an 
orangy hue skin color, but I think it looks 
better when dried. My opinion, anyhow. Brown to 
white will give you a more tan color, while the 
light brown looks more bright and has some 
red/orange undertones. It's also easier to darken 
for shadows (again, in my opinion).

I also use Anita all-purpose craft paint 
(naturally I do not mix the two brands/mediums) 
and if you're using them, there's all sorts of 
colors to try for flesh. Depending on the 
character you're painting (or the scene, etc) you 
can play with various forms of skin tones. 

"Beige", "Buff" and "Barely Pink" work well with 
pale colors (or lit shades)... but they are 
definitely PALE. And hard to darken (I added 
brown to buff once - and got a deep caramel-y 
color which doesn't necessarily look bad, it just 
doesn't look right), so be careful. For dark, tan 
skin, you could try "Latte". 

Then there's all sorts of light orange 
colors: "dusty peach", "blush", or just plain 
old "peach"... 

When I ranted about screwed up flesh tones on 
here, Pharna-san suggested I add a touch of green 
to my mix for a more "alive" look. It keeps away 
the sallow look, but too much causes a nauseous 
color, hee.^^

Your best bet: experiment, trial-and-error, patch 
test mixed colors. You'll get there, and you'll 
be all the more wiser for it. ^_~

Good luck!
~ keeper

P.S. Here are some of my fan cels that I 
experimented with flesh colors, for reference. 
The first one, Nagi from "Weiss kreuz", I painted 
in vinyls. His flesh is brown and white. The 
second, stripping Olba from a "GX" yaoi 
doujinshi, is in Anita crafts and blush and 
white. Hope this helps! ^_^