You can’t preview the colour shaders before you buy them in Destiny, unfortunately, at least not officially. Unofficially however, you absolutely can preview all the shaders if you want to see how they would look on any of your characters.
Talented people over on Reddit have made a website that lets you preview any of the available shaders, by actually applying them to your characters. So no more guessing or losing too much money when you buy one you don’t like.
Here’s my Titan sporting the Chatterwhite shader for instance:
Have a go yourself on the website, you just need to enter your PSN ID or Xbox GT.
Source: Destiny Website.