Dear Bert,
I hope that I can help you:
open "ardublock-allxxx.jar" wirth WinRAR,
drag and drop "ardublock.xml" to your desktop,
open "ardublock.xml" with a Editor like "notepad++",
scroll and detect the block which you want to change - you look for a line like this: <BlockGenus name="glue_poly" kind="data" color="245 245 245" initlabel="bg.glue_poly" editable-label="no">
the color is a RGB-color, for examle 245 245 245, change the numbers,
save the file,
drag and drop it back from the desktop to WinRAR,
start arduino IDE- if everything is correct, you can start ArduBlock,
if you made a litte mistake, ardublock will not appear.
Good luck
Grüße aus Deutschland
Christian