Site-tool change colors

Hello, I want to make a site AS ONE that already exists, I am not owner of that site, it will be only as your reference, the address is in the attached file. Just go there to understand how it works, it's simple, consisting of a single page. On this site you can load any JPG image, usually in black and white, and change them with two colors of your choice. Afterwards it is possible to download the image file with the colors changed and the resolution remains the same as the image loaded previously; for example, if the loaded image has 300dpi, so it is returned. Note: - to upload the image file you need to do the LOG-IN, with email and password, I do not care that users have their own account, just enter an email (if possible will be collected in a specific folder) and password is unique to everyone, of course it will be provided before going to the site. - the part below regarding the "SHOWCASE" of the articles, changes an article every time, I think like every half hour, or in its outline (4 lines by 5 columns) puts a new article on the top left, the others " they flow "and the last one on the bottom right goes away. This is fine with me, if you know other similar and / or better ways do it, but I ask you if it is possible to have, instead of more lines dedicated to a single store, that for each line there is a "sliding" of articles of a store different from that of the other lines, that is, each line is dedicated to items in a shop different from the previous one, and all the lines in each of the times change automatically. In summary, the operation of color change must be the main issue, it must be quick and efficient, then obviously usability, the instructions must be as clear and immediate as possible for users. As for the aesthetics / layout if you have any idea to propose is welcome, the site that I have provided as a reference is already quite essential, has everything that there must be, but if you know how to improve it in originality, modernity etc ... do not hesitate to propose your ideas. Indexing and ranking on search engines is NOT required. Do it easy. For any questions I am available. Thanks, Alex