The 'hot' colormap has white at one end of its scale and almost-black at the other. Suppose you successfully change things so that R=1 is white. What do you want to happen for values of R that are greater than 1, which occur in both plots?
If you are ok with all values of R >=1 mapping to white, then using the line
just after the plot command does so, where Rmin is the minimum value of R over the entire set of x,y values.