Blue stands are part of a three phased expansion program to facilitate the larger aircraft at LCY. Three Blue stands are marked up over 7,8,9 and 10 and are called 8A, 9B, 10B. These can be used by any aircraft but allow the E190 to be parked on them. If a aircraft is using stand 7 then 8B is not available for use. If long term parking of a E190 is needed it will be placed on 10B. Stand 9 can then be used with reduced width if pushed back with a tug and 8 and 7 are available as normal with non E190.
I hope this makes sense. Airfield ops has a nice diagram if you need more info.