see below youTube link to a video the oven is fan assisted and has recently been cleaned. there is a big fan at the back circulating air inside the oven stoves oven flame - YouTube
That looks fine. Flame colour can be affected by the metal that the flame plays onto - I suspect the yellow on the left is a result of where the flame plays onto the metal of the thermocouple. As always - if in doubt, get a gas qualified engineer to take a look at it.
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