Blogger recently implemented a feature (a rather poor feature, at that) which automatically “enhances” all your images. This causes all white backgrounds to show up with an unattractive grey/beige tint. Follow the steps below to solve this issue.
1. Go to https://www.google.com/settings/plus.
2. Scroll down quite a bit to locate the Photos section.
3. Within that section, there is a subsection titled “Auto Enhance.” Check the Off option. The setting should automatically update. If you’ve already uploaded your header, you may need to re-upload it to remove the tint.
Note: You MUST have Google+ enabled to access these settings. If you don’t have it set up, click here to get started. Just go through the signup process and then follow the above steps.