Right you are. But if you have qlikview available you could generate the expression in Qlikview and copy it over to the Qlik Sense app. The Colormix functions are available in Qlik Sense too.
But there's another option that is a lot simpler. You can set the Colors setting to Custom and choose By Measure and select one of the four gradient options.
In qlik Sense 2.2 you can use the colormixx function
See my post here with qvf example :
the file attached gives examples of how to use variable color to change all the colors of charts and table
ColorMix1( rank(total [your measure expression here])/noofrows(TOTAL) , rgb(15,97,119), rgb(36,242,197))