Thank you for using FUMA and for your message.
When viewing the plots, if you scroll down there is a message explaining why the colors are gray:
eQTLs: When eQTL mapping was performed and if there is any eQTL in the selected region, all eQTLs with user defined P-value threshold and tissue types are displayed. Of those eQTLs, eQTLs which did not used for eQTL mapping (eQTLs that were filtered by user defined parameters) are colored grey.
I hope this helps,
Tanya