I've just posted a query about Mac plugins which may serve this role but it occurs to me that Mulch, with it's strong focus on live on stage performance, may be predisposed to such a feature.
Basically a silent metronome which uses a graphical display of the pulse and the beat position within the bar. Xoxos blinker plugin is a fine example, allowing some configuration of the amount of blink but i must say it's black and white colour scheme is fairly full on and i felt like i was in an interrogation scene within a kubrick film.
Ideally something resizable and either tied into the dark and forthcoming lighter mulch colour schemes or color configurable.
For me, this in addition to a tap tempo functionality would be quite handy in moving between playback active and inactive states, particularly with mulch's ability to generate and process sound with the clock stopped.