colour printer." Here, because of the ambiguity as to whether only is modifying "seems" or "when he lets in yellow", it should be placed immediately before "when" if that is the intended meaning. Fowler offers the following advice:

There is an orthodox position for the adverb, easily determined in case of need; to choose another position that may spoil or obscure the meaning is bad; but a change of position that has no such effect except technically is not only justified by historical and colloquial usage but often demanded by rhetorical needs.