Depends on the variety, not soil acidity.

Yep, variety - but they also come in pink, yellow and pink/white streaked.

Thanks, Owdboggy and Bamboo, for your prompt replies!

Okay, what about hydrangeas - does their colour depend on soil acid ir alkali?
Jeez, what a pain, this guy!

thanks!

To some extent, yes, particularly with blue, and sometimes pink, varieties. In neutral to alkaline soil, blue ones look more a sort of drab lilac - in acidic soil, blue will be proper blue, but pink may be lilacy, or it may be fine.

Agreed, soil acidity/alkalinity tends to intensify the already existing colour. That is in H. macrophylla, in the other species it makes no difference to the flower colour at all.