Lighting, Light Fixtures, Ceiling and Exhaust Fans - Light Fixture

I have a basic question...I don't know anything about electricity.

I bought a house and one of the rooms does not have a light fixture but i had one before. There are 4 cables hanging from the ceiling, a black one, a red one, a yellow one and the cable wire. I bought a light fixture but this one only has 3 cables, one black, one white and the copper. My question is:
The white wire from the light fixture does it go with the red or the yellow wire in the ceiling?

The white from the fixture should go to the white or grey in the ceiling. Since you don't have either I am going to guess that the yellow wire is possibly a white that has yellowed with age. Does that seem possible or is it definite a yellow wire?

The wire is yellow.

Then you have non code compliant wiring or some one has removed the white and you need to pull it back in. It sounds like, from your wire descriptions, you have conduit so that should not be too difficult.

Karcis, What country are you from?