Custom graphics are easy to make compatible for web posting. The most common format that is compatible with almost every web hosting service is the .jpg format. Most scripts are written to accept .jpg files. The next most compatible format is the .jpeg. Either of these formats are easily added to HTML, PHP, Gimp and other platforms. Coding in HTML is popular for simple websites. The graphics should be designed with the highest resolution possible for the best quality and clarity.
Colors can change when items are saved for web usage. It is always best to add the right lighting to highlight the focal points of the graphic and use a shade that is just a tad brighter than the client wants so that the image permeates the right color palette to the website through the coding process. The size of the image can also play a part of the color transferring properly. Try designing with pixels instead of inches as your image size. The properties of each web page are easily attainable along with the space provided for the image. Compatibility is easy when the right format, size and integration are put together properly in using custom graphics on a website.