Do keep in mind, there is no lore preventing dragons from using the light or shadow. Or any divine magic at all.
But in Heartwing, we have the headcanon enforced. That dragons would not use the Light or any divine magic simply because that is not what they believe in. In order to use the divine magic, you have to be a believer, and dragons believe in the Pantheon and Titans, which does not use Divine Magic at all. Which would contradict itself.
However, it is completely allowed for a red dragon to use arcane magic. As evidenced by Korialstrasz (Krasus) as he was a member of the Council of Six in the Kirin Tor.
[Alive] Aerenstrasz - Leader of Heartwing
[Alive] Aerdranstrasz - Child of Aeren
[Alive] Azraelstrasz- Second son of Asherystrasz - Not part of Heartwing
[Deceased] Asherystrasz - Retired leader of Heartwing
[Deceased] Hydrastrasz - Former Leader of Heartwing