sRGB IEC61966-2.1.

sRGB is the RGB colour space most monitors, browsers and design applications assume, and sRGB IEC61966-2.1 is the ICC profile that describes it, the string a designer sees in the save or export dialog. Printful asks for it by name, says its printing systems are optimized for files with an embedded sRGB profile, and warns that Adobe RGB or ProPhoto RGB can cause unexpected colour shifts. The mistake runs both ways. A photographer uploads a wide-gamut file to a pipeline that reads it as sRGB and the colour moves; a designer converts to CMYK first to be safe and throws away gamut before the RIP ever sees the file. Converting is right only where the shop says so: Transfer Kingdom wants CMYK and Transfer Superstars wants it converted with FOGRA39 on DTF, and SAIC's print bureau asks for Adobe RGB 1998. Neither shows on the uploader's screen, so the first anyone hears of it is a sample that does not match the approved mockup.