Official colour specifications can be found at the Open Data portal of the Île-de-France Mobilités website (under the Prescriptions Signalétiques section).[1]
The official RGB values in the document must not be used, because they are noticeably oversaturated, in addition to never being used in practice by either IdFM or RATP. Instead, use RGB values that were generated by converting official CMYK values in Adobe Illustrator, under the European General Purpose 3.1 colour profile.