Yes! Blue shoes are an awesome idea for a wedding! You're absolutely right about them not showing -- yet they're perfect for your "something blue" because of your love of shoes. Rock on!

If you're nervous about them not turning out right (I dyed a dress light pink and it turned out dark purple once!) you might want to get those dyeable shoes where you send in a swatch of fabric and they dye the shoes to match. They do that for bridesmaid dresses.

If you want to DIY, it's good too - don't worry about them too much, though, 'cause they won't show.

As far as telling your mom, just explain that it is important to you that you be yourself and that this is not really something she should have an opinion about. They're your feet -- she won't even see them! If it continues to bother her, just make it clear to her that you will be putting on your shoes in "private" so that you don't "upset" her. Act like a rebellious child sneaking around if you have to. She'll realize how ridiculous of a battle it is and back off.