Trade dress is protected in addition to the actual brand marks.

https://en.wikipedia.org/wiki/Trade_dress

IKEA is the only furniture store with a four-letter name in that same typeface in yellow on a blue building even though it is called 'STYR' here. It is the only furniture store using that uniform, also blue-yellow, for its personnel. The game maker clearly used IKEA as an inspiration but forgot that 'inspiration' is not the same as 'duplication'. They could have made the building red, used a serif typeface and a 7-character name, dressed their 'personnel' in red-green uniforms, etc. and IKEA would not have bothered them. Now, they did, and right they were.