We present a ver­sat­ile tech­nique to con­vert tex­tures with tri­s­tim­u­lus col­ors in­to the spec­tral do­main, al­low­ing such con­tent to be used in mod­ern ren­der­ing sys­tems. Our meth­od is based on the ob­ser­va­tion that suit­able re­flect­ance spec­tra can be rep­res­en­ted us­ing a low-di­men­sion­al para­met­ric mod­el that is in­trins­ic­ally smooth and en­ergy-con­serving, which leads to sig­ni­fic­ant sim­pli­fic­a­tions com­pared to pri­or work. The res­ult­ing spec­tral tex­tures are com­pact and ef­fi­cient: stor­age re­quire­ments are identic­al to stand­ard RGB tex­tures, and as few as six float­ing point in­struc­tions are re­quired to eval­u­ate them at any wavelength. Our mod­el is the first spec­tral up­sampling meth­od to achieve zero er­ror on the full sR­GB gamut. The tech­nique also sup­ports large-gamut col­or spaces, and can be vec­tor­ized ef­fect­ively for use in ren­der­ing sys­tems that handle many wavelengths at once.