That's just how trademarks work, feel free to argue with your associated government entity to change the laws. It's the same way that UPS has their color brown trademarked and t-mobile's magenta trademarked.
In particular, the international registration number that UCI has for their
'rainbow stripes' trademark (pdf link to their license program) is 1032330. Looking it up via the
international registry shows the related goods that the trademark is for:
591 Information concerning colors claimed
Blue, red, black, yellow and green.
Bleu, rouge, noir, jaune et vert.
Azul, rojo, negro, amarillo y verde.
511 International Classification of Goods and Services for the Purposes of the Registration of Marks (Nice Classification) - NCL(9)
12 Bicycles and bicycle accessories included in this class.
25 Footwear and clothing, particularly for cyclists.
41 Organising sporting activities particularly competitions involving sport, film production, publishing.