I think it's still too early to judge the lurker.
We are all experienced in Starcraft 1. We see the Lurker as follow :
It looks like a big and ugly creature. Till this point, I agree with you, the design does not fit. The colors are strange.
However :
If you consider the overall layout and design of background and effects of Starcraft 2, the Lurker fits accordingly. The color matches the new platform and other zerg units.