Ah, I see what you mean. That’s not how it’s intended to be used. But you can create your own gradient by chopping the inbuilt one in halves:
magma = cgrad(:magma).colors
c1 = cgrad(magma[1:15])
c2 = cgrad(magma[16:end])
h1 = heatmap(1:10, 1:15, rand(15,10), clim=(0,0.5), c = c1)
h2 = heatmap(1:10, 1:15, rand(15,10), clim=(0.5,1), c = c2)
plot(h1,h2, size=(800,400))
