Woo hoo!! I love my I-pad!!
I have one quilting app ... but there are more. Mine was a free one called "BlockFab-HD"
The one I have has several different blocks you can choose from (perhaps 50). You can change the colorway in the block to see what you like (about 20 different choices), it gives cutting directions for each block including yardage.
You can place the block in a quilt, tell it how many blocks across and down - and it will again give cutting directions and yardage.
You can choose two different blocks and either pair them together (block A next to block B - and so on), or "combine" them (block A inside block B - and repeat through the quilt) and again cutting directions and yardage.
In the quilt view - you can drill down on the cutting directions for each piece of the block (for example "cut 48 half square triangles) and it will give cutting directions (cut 2 strips 2 7/8 wide, cut 1 2 7/8 squares from each strip, cut each square in half on diagonal).
You can change the colors on the quilt view as well as the block view.
You can add sashing as well (I don't think you can get cutting/yardage on the sashing - I think it's just to show you what it would look like).
Oh, you can also convert from inches to metric.
I would love to be able to choose my own colors individually - but the colors are just "combinations" that you can select. It does give you an idea how it looks in blues - or light vs dark in each piece of the block.
It's a neat free program that is OK for getting ideas like secondary patterns from two different blocks, or colorways - but it's not a program I would rely on to design a whole quilt.
I purchased this one a few years ago, have not looked for quilting app's since then. There might be better ones out there now.