Tanaka kar98 colour?

Are you trying to change the wood on your Tanaka to another colour or are you trying to copy the yellow colour that a new Tanaka has do a different piece of wood?

If it's the first you need to sand ALL of the coating off the existing wood (most of the woodwork can be removed from the gun) then use a wood stain. I used rosewood for mine. Let it dry and then keep applying new coats until you are happy with the colour or until the wood stops taking any more dye. I rubbed beeswax into the wood afterwards to make it a bit more water repellant.

If it's the second then it's woodstain again - but remember you can only stain wood darker, not lighter.