Does this do what your want?
import PlotlyJS
const CS = PlotlyJS.PlotlyBase.ColorSchemes
test_x=vec(collect(1:2:30))
test_y=vec(collect(1:10))
rand_test = Matrix(rand(10, 15))
p = PlotlyJS.heatmap(x=test_x, y=test_y, z=rand_test, colorscale = CS.grayC)
PlotlyJS.plot(p)
q = PlotlyJS.heatmap(x=test_x, y=test_y, z=rand_test, colorscale = CS.grays)
PlotlyJS.plot(q)