Why is my sweet pea only red flowers?

[MadYoke]

I grew it from seed I harvested from last year's plants, they were different colours. Now there aren't many flowers yet, maybe the red blooms first or something? Novice gardener.

They do tend to revert to the mother plant. The seed don’t necessarily come true to what you collected them from which was possibly a modern hybrid.

either way you got free flowers so enjoy 😊

Yes, might depend if original seeds were F1/hybrid: https://www.rhs.org.uk/vegetables/f1-hybrids

Thank you! I just assumed they would look like the parent

If the plant is a hybrid between two other varieties, it probably won't produce seed anything like itself. It is more likely to resemble either one or other parent, or some other third variety that it cross-pollinated with.

Hybrids tend to have characters intermediate between the two parents. For example Geum rivale x G. urbanum often has nodding flowers like rivale, but yellow like urbanum.