Nintendo has sued ROM sites (e.g., RomUniverse, LoveROMS) for millions of dollars. Hosting or downloading a Paper Mario Color Splash ROM Europe could put you at risk. More realistically, your ISP may send a warning, or the download site may infect your PC with malware.
The primary reason players search for the European ROM specifically is language accessibility. Unlike some regional releases that are locked to a single language, the PAL version detects your system settings to provide a localized experience. Additionally, for those playing on an original Wii U console from the UK or Europe, a PAL ROM is necessary to avoid region-locking issues unless the console has been modified. Gameplay and Graphics Paper Mario Color Splash Rom Europe