[metapost] color stack overflow

[Akira Kakuto]

> with EssaiNew.mp, I have the "color stack overflow" error ?
> (and what is the signification of this error ?)
>
> with EssaiNew.tex, I have no error.

Both in the latest MetaPost and in the MetaPost 0.641,
max_color_stack_depth = 10.
So it cannot make .mpx file for your example.

I have confirmed that there is no error with
max_color_stack_depth = 20.

Best,
Akira