There are lots of potential causes for discoloration and buoyancy issues. Many (most) of them are from minor health issues. For example, your Betta's buoyancy issues could simply be due to constipation or overfeeding.
I recommend that you start a new thread for your Betta. Explain what's going on. Copy and paste the information from this sticky
into your post so we have a clear idea of what's going on.
But again, what you've described so far sounds like a minor digestive issue which might require a day of fasting or a food brand change.