colours

So for some reason some of my signs are grey and some are white and I don't know why. Is there a reason for this or is it just some visual bug?

So it's been kinda bothering me, cause the default sign text colour is so unreadable that you need to really be patient to read it. It's not as big of a problem for me, cause I can change it with & (using precious space tho) but most of the players can't do anything about it, which is kinda...