This is the landlords problem . Don’t paint unless you have permission in writing

Ask the landlord what they want to do

If you really want to paint ask the landlord what colour could be a standard colour

Ask the landlord to pay for the paint

The better context is that the Landlord is happy with mismatched fence panels. If you're not satisfied, you can pay for it yourself.

Do expect shenanigans with your deposit if you paint them all hot pink, lol. Unless it is in writing, the "consent" you got to paint them will undoubtedly be denied ever happened.