It's common wisdom that programmers can only create code and designers can only create art. I think this has come to pass because there is an artificial line drawn in the sand by developers and designers between planning and implementation. Regardless of if this is because of laziness or territoriality, I think that it doesn't need to be so.
Here is a simple way to get started learning to think like a designer so that you can take a mediocre (but highly functional!) web application and turn it into something marvelous:
Read Picture This
Picture This helps teach you how to think about colors and shapes in images in what I believe is the simplest way possible. As silly as it sounds, I gained a lot of insight from this book that I would not have otherwise been able to learn on my own easily.
Read Don't Make Me Think!
Don't Make Me Think! is a great primer for learning how to improve User Experience in every website you work on. Don't be fooled by how old the book is. It is still very relevant, and how well the book holds over time is a testament to how universally true it is.
Practice a bit
Download GIMP or Inkscape and try to design your own logo. Think about what you want to communicate to other people about yourself.
Rewiring your brain might hurt a little, but I promise it is worth the effort.