I really like denim and I think it would work well as your darker colour, with cloud blue as your light colour. In my opinion aster is quite bright and would provide too much of a contrast to denim and cloud blue.
What about parchment to match the neutral colour in the fabric?
I should have said earlier that I also want to use cream, silver and parchment. And red. We have a big red wardrobe so I'm going to include that. I think I need a bolder colour to tie in with the red iyswim. Hence me wanting a third shade of blue.
I'm sure I've got a small bit if aster upstairs, it's definitely not purple though.
Oops. Meant to add a pic of the pattern. It's honeycomb afghan by kazuko ryokai. The picture in the book has many colours. This pic is one from the ravelry projects page for this pattern. I like the colours but it's too muted for me, I want to add in a couple of bolder/ brighter shades.
Thanks to the marvels of Facebook I remembered the lovely lady at My Craft Life and got her to pick out some colours for me. I'm quite excited to squish my new yarn. But will probably be back to ask how to organise the colours into my pattern.