"Red, yellow, and orange are fall colors."
Translation:Červená, žlutá a oranžová jsou barvy podzimu.
red (noun) = červená barva = červená, etc.
Here "červená" is an adjective used as a noun.
The standard ending for a feminine noun like "barva" in the nominative singular is -a, not -é. Cf. "žena".
The standard ending for a "hard" adjective in the feminine singular nominative is -á, not -é.
So -é does not enter the picture here; it is the hard adjective ending for neuter (not feminine) nominative singular.