When viewing orthoimagery (any RGB imagery really) you can set Just One 3 band color (say R=0, G=0, B=0) to display as null/transparent in the Properties>Symbology tab. This is a nice feature. Unfortunately it does not fix all the problems in collars, noise, etc especially if the imagery has been compressed or othwise processed causing bleed, smoothing, or generalization. Currently you have two Options inside of ArcGIS: 1) Classify and stretch your data (degrading quality significantly) and then setting values to null 2) Use the Raster Calculator to recalc values - takes a long time and uses a lot of memory&storage especially if dealing with a lot of imagery from different sources. (Masking can help but it does not always clean up the edges, does not work well on noise inside of images, and can take time to create.)
Solution is generally simple - add a button that allows the user to input a list of values...say 0,0,0, & 0,1,0 & 0,0,1 & etc...It would be great to be able to save/load this list and perhaps specify separate displays for each but right now I just need to access multiple values.