When making minimalist bifold wallets like this one, I usually soft leathers with pigskin lining, or none at all, and the colors are always more traditional such as black and brown.

However, this time I wanted to make a very striking wallet using a clear blue as lining inside the deep blue main body leather. 

At the same time, I also wanted the wallet to look sport, rather than a more serious looking wallet. This is something I've explored in the past and can easily be achieved through small changes in your designs, especially in the use of a contrasting thread. 

So while the deep blue makes the wallet look serious enough, the clear blue thread gives the wallet a sensation of freshness, so to speak. Keep in mind though that these contrasts are very showy even from far away, so make sure you always make a test of contrast before working on the real project to see if that's the finish you want to achieve. 

-David