scale_colour_gradientn color limits gives a constant color

Question

I am trying to limit the color in my scatter plot by using limits = c(value_min,value_max) but all the values outside the chosen value_min/max become grey.

Is there a possibility to assign the values of points outside of the thresholds to be the same as min/max values?

Here is part of my code:

ggplot(rows_4D_Variables, aes(x=sp_x_prm4, y=sp_y_prm4, col =avg_nrms, shape = a)) +
geom_point(shape=19, size = 1)+      
scale_colour_gradientn(colours=jet.colors(256),limits=c(0,75))