To change the colour that an element highlights when you snap to it, use this keyin:

set hilite [colour]  Where the colour option is one of the following:
black, blue, cyan, dgrey, green, lgrey, magenta, red, white, yellow

In the V7 versions of MicroStation, you can use the following keyin to open a handy picklist that allows you to select the colour graphically:  MDL LOAD HILITE 0    Note that this keyin does not work in any of the V8 versions.