Jim,
(1) Deducer uses ggplot2 for plotting, so for control of colors you want to read up on scale_brewer, scale_gradient, etc. at
http://had.co.nz/ggplot2/ or pick up a copy of the ggplot2 book. Generally, yes, you would use some variable to color the data. This may be thought of as a third dimension (which can be either continuous or categorical) to the data, plotted in color instead of on a z-axis.
(2) You can extract the call from "Tools"->"View call" if you want to edit it before running it (and for some operations, like sorting data within the call to ggplot, you may need to do this). You can also get the code from the console window after clicking "Run" in the Plot Builder dialog.
Hope this helps,
Tom