"Je tvá oblíbená barva žlutá?"

[ChrisHull14]

I answered "Is your favourite colour yellow?" and it wasn't accepted.
The only thing I can see different is my spelling of colour, as opposed to the US spelling color.

[endless_sleeper]

It should be accepted. If you encounter the same problem again, take a screenshot and file a bug report here.

[ettoreg60]

I answered "Is it your preferred color yellow?" and it was not accepted.

[VladaFu]

Why would you put the "it" there? I do not think it is correct.

[Randonneur3]

I look at this simple sentence with very little familiarity. Czech is so different! (One week so far learning it.)

[Janice580199]

Color is spelt colour in Australia, think it should be corrected and accepted! Unfair to be failed for it.

[VladaFu]

Brittish spelling is accepted automatically by Duolingo software. If you think it is buggy, report a bug to them.

The people responsible for the software certainly do not read it here.