One of those handy, little-known features of JMP that's been around for a while is the "Color or Mark by Column" command in the Rows menu.
You pick a column from your data table, and JMP will apply colors or markers to each row based on the row's value for that column. For numerical columns, you can indicate whether the colors should be categorical or follow a continuous gradient. And there's more -- it will also generate a legend in a separate window.
For example, here is a legend created by the command that's goes with the plot of the earlier scatterplot colored by age.
In this case, I had already custom-colored the row states, and those colors were maintained since there was already a unique color for each value.