When doing 2 color changing round stars, is there a rule of thumb on outside's color thickness to inside's?



I'm trying my hand at small color changing stars.
Doing a ruby red/emerald green metallic that uses Strontium nitrate,
barium nitrate as only differences in comp.
Used red as a coreless with NC, to around 3/32-5/32 round dia.
To get equal amount of time per color would it be : core dia=outside
layer thickness?
Not using changing relay either 'cause I don't think it would lite the
red, so choreography is out the window.
Right now the green jaw breaker layer is about 1/5 the OD of red core.
Trying to duplicate Bradford pear autumn color.
Hopefully.
Any help please.
Dan
.