Ok, this bit is quite cool. You have painted over your tiles and they look a bit flat now, because there are no grout lines, but you can add these back in with a grout pen. Grout pens are not long-term solutions to anything, they are basically just paint that freshens up the look of your grout, but in this case they are perfect. Fiddly, yes, but easy to do too. You can get grout pens in different colours, but white is the most common. If you would like a nice dark grey, for instance, you may have to search a bit online, but grout pens are cheap, so buy a few and experiment if you like!