Thank you all for the feedback! I figured that this theme was not really subtle, but I am glad to see that people do not find it extremely tacky either. :) I probably would only end up using a few of these names mixed with some others that were not colors.
@sidura: I'm glad you like Hazel and Lilac together! Hazel is a long-time favorite and there is a good possibility that I will eventually end up using both names. I think the fact that both names have a nature association and a color association makes them less tacky for siblings.
I prefer more subtle links - Sybille Iolanthe and Violet Apolline, for example, which both have 'purpley' English names and French double -ll names. But a colour theme could work if you were subtle enough. The problem with themes altogether is that it becomes harder with each child to find a name which fits the theme, but you love just as much as the first one...which is why Berries like to plan ahead I suppose :) Good luck.
@lexiem: Thank you for those subtle color name suggestions! This thread is generating the kind of brainstorming and discussion that I was hoping for.
Bonnielyn - it's too bad they choose such an obvious color name like Teal. I think it's a bit harder for boys but they could have kept that theme going without anyone really noticing. Also... your neighbors need to name their next child Lincoln alla Lincoln Belle Shepherd who basically was named after a car.