The effect of a frume is to reassign selected token colours across the manifold. Up to five colours may be replaced using a single frume. (On web-based fora, a useful notational convention is to colour the letters of the word 'frume' according to the token colour substition(s) being performed.)
The frume is a very useful way to recolour one's own tokens to suit the stations they now lie on, and simultaneously change the colours of one's opponents' tokens in a way that may severely disrupt their play. When used correctly a frume can be an extremely powerful action.
Countering a well-planned frume can be difficult. Triggering a token cascade is an obvious tactic, but few players who use the frume will leave their opponents with the right colour tokens to perform such a move. Playing another frume to reverse the first is rarely possible, because one will usually have lost the token colours needed to play the reverse. Moving rapidly to a holding station and replenishing one's token stocks is usually the simplest fix, but this of course gives the fruming opponent one or more turns with a free hand, which will usually have been the intended object of the frume play. Expert players usually switch to a low-token or entirely tokenless strategy for a while, until their token reserves have built up again; the use of glides and rataches places less strain on a suddenly-limited token supply. This technique is known as a revanche.