Sometimes I get the interpolation in the ramps...but most of the time i do not...and honestly I do not know why I sometimes get it..Im always in 8 bits...its the effect gradient Ramp right?..but you can change your bi deptth by ctrl clicking on the little 8bpc in the project window
add the gradient ramp effect (you only get 2 colors, i'd keep them back and white, but you can change the location of the end points for angle, and ramp shape).
then add colorama to colorize the ramp. the default will give you a smooth rainbow or colors. twirl down the output cycle and near the bottom of those settings uncheck the interpolate palette. the smooth rainbow will be replaced with solid bands of 6 rainbow colors. now you'd just need to change the output color cycle to the colors that you need (which can be tricker than you'd think)
this isn't an ideal workflow, but it may work for you.