This is a very good question and it deals with a nightmare many musicians face - monitoring. But since it deals with much more than that, I'll try to expand the answer to cover general principles in playing live with a band (from the keyboardist's perspective) - some of which may not answer your question but I find it helpful. Would like other keyboardists to chip in here.
There are 3 general principles:
1. Playing techniques
2. Choice of patches/sounds
3. Sound engineering
1. There are a few playing principles I apply to prevent "muddiness" or lack of clarity in playing (esp for pads):
(a) Sonic space. I stay clear of certain instruments range when playing certain patches. This also includes the range of the vocalist (soprano, alto or tenor). You would very rarely play with a bass solo vocalist. I stay clear of the range of the vocalist/instrument so there's no competition in the same sonic space.
(b) Open vs close voicings. Depending on the need for the song/choice of patches, I play my voicings accordingly. Generally speaking, if I want to avoid muddiness, I would use more open voicings particularly for pads (ie don't play the notes so close together but spread them apart).
(c) Note that some songs call for "muddiness". In these cases, esp when playing slow sustain low-string type of sounds, it calls for discernment. Sometimes, pads are meant to be "felt" and not "heard". It's there to create an atmosphere for the song. Remember to hear the entire band, not just yourself. Hear the others as well and create something for the entire band.
2. Choice of patches can help. Pads need not necessary means bassy and muddy. There are sweeps, saw etc that cuts across the band. The choice of patches depends, of course, on the song. But my selection also depends on the acoustics of the place. A large echoic hall calls for a brighter sound compared to an anechoic concert hall/studio. Instead of fiddling with the EQ too quickly (I leave that more for the sound engineer), I first select the right patch based on the brightness. This goes for other non-pads sound - brighter or darker piano for example. EQ is a last resort (esp for some keyboards that allow you to adjust the EQ on the fly). I always try to tell the sound engineer if I'm going to adjust the EQ.
3. I work closely with the sound engineer. I leave everything live to him. But for monitoring, it can get tricky. The basic principle is not to share your monitoring amp with somebody else if possible. But we may not have that privilege many times. I had to play with the monitor blasting every instrument (vocals, bass, guitars, keyboards etc) - you can imagine that you can hardly hear yourself. Therefore....I ALWAYS bring along earphones to monitor myself in case these situations arise. I have tried all kinds of ear monitoring and my preferred method is a simple earphone that doesn't fall out of my ears easily. In-ear monitoring (earphones with the rubber buds that block off all external sounds) are not good for me for a few reasons:
(a) I can't hear the other players well except myself
(b) many times I sing along or hum while I play - which is a disaster as you hear muffled voice, even if you have only one side on.
The other option is headphones - but then it doesn't look cool...(even though I bring them along in my gig bag as well). So the answer for me is a simple earphone. If you use more than one sound source (multiple keyboards/ sound modules/ samplers etc - like me), then it calls for a personal mixer. This gets tricky for the sound engineer, so I don't mess with it too much in terms of EQing - just the right volume in terms of balance of the different sound sources. I leave everything else to the sound engineer to fix.