I dont think it makes a difference. Yeah when I tried it one of mine turned white against black background when dry as well.
Then I picked a BD on eBay and the slurry does indeed look different. More dirty looking with yellow tint.
I am not very good with colors so when I see an Escher by itself I cant say I can pinpoint them.
When you line them up it becomes more obvious.
First pic dry, second wet. From left to right - light green(I presume), BG (has a sticker), Yellowgreen(barbers delight), dark blue(I presume).
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