PNG was a file format that, among the original reasons for conception, was created to show the same color over different computers, with different OS’s, and browsers. To this end, gamma, or lighting, correction was added. While solving the original problem, a new, bigger, badder problem was created. Now, there was the potential for color inconsistencies on the SAME web page. For example, the color of certain items rendered on the page with the same hex value will display differently than PNGs rendered on the page painted with the same hex value.
Sometimes bland text on a webpage needs a little spicing up with an image. Instead of having to mess with markup, this text can be replaced with an image. Plus, the remaining text in the markup allows for better screen-reader access. There is a fair amount of discussion on the best way to do this. One of the ways that I’ve found works pretty well for me is what is known as the Leahy/Langridge Image Replacement (LIR)