Ok so it seems that a blue can reveal a blue.
I am quite amazed how precise a character with Detect Hide has to be to reveal a character with Hiding @ 100 - this might just be a good thing for you to know dan but a character with 100 Hiding vs 100 Detect Hidden you have to target THE EXACT tile that the player is hiding on... if you are even on tile off of where the player is hiding it will not reveal the player..
Now this changes when I drop the Hiding to 99.9
When I drop the players hiding to 99.9 I can reveal that bitch targeting a tile like 6 tiles away it will reveal him 100% of the time, so basically unless you have 100 Hiding a player with detect hiding will shit on you... the being said detect hiding is almost useless if you are going against someone with 100 Hiding because if they are stealthing knowing exactly what tile they are on is going to be a bitch and a half - even with Tracking.
Also I just want to let you know that I did make my character with hiding go grey and then hide and revealing chances all seemed to be the same blue or gray it didn't effect anything.. this makes me assume the same for reds.
This might be something worth checking into to make sure its the same, I don't know all the details on RealUO but this is the results of what I have done while I was in Fel.