I tried many colormaps with matplotlib.pyplot, but most of them give similar errors. Here is an example for a grey colormap.
import colorcet as cc
import matplotlib.pyplot as plt
# Neither of the following work
plt.set_cmap(cc.m_linear_grey_0_100_c0)
plt.set_cmap("cet_linear_grey_0_100_c0")
plt.set_cmap(cc.cm["linear_grey_0_100_c0"])
plt.imshow(arr)
ValueError: Colormap linear_grey_0_100_c0 is not recognized. Possible values are: Accent, Accent_r, Blues, Blues_r, BrBG, BrBG_r, BuGn, BuGn_r, BuPu, BuPu_r, CMRmap, CMRmap_r, Dark2, Dark2_r, GnBu, GnBu_r, Greens, Greens_r, Greys, Greys_r, OrRd, OrRd_r, Oranges, Oranges_r, PRGn, PRGn_r, Paired, Paired_r, Pastel1, Pastel1_r, Pastel2, Pastel2_r, PiYG, PiYG_r, PuBu, PuBuGn, PuBuGn_r, PuBu_r, PuOr, PuOr_r, PuRd, PuRd_r, Purples, Purples_r, RdBu, RdBu_r, RdGy, RdGy_r, RdPu, RdPu_r, RdYlBu, RdYlBu_r, RdYlGn, RdYlGn_r, Reds, Reds_r, Set1, Set1_r, Set2, Set2_r, Set3, Set3_r, Spectral, Spectral_r, Vega10, Vega10_r, Vega20, Vega20_r, Vega20b, Vega20b_r, Vega20c, Vega20c_r, Wistia, Wistia_r, YlGn, YlGnBu, YlGnBu_r, YlGn_r, YlOrBr, YlOrBr_r, YlOrRd, YlOrRd_r, afmhot, afmhot_r, autumn, autumn_r, binary, binary_r, bone, bone_r, brg, brg_r, bwr, bwr_r, cet_bgy, cet_bgy_r, cet_bgyw, cet_bgyw_r, cet_bjy, cet_bjy_r, cet_bkr, cet_bkr_r, cet_bky, cet_bky_r, cet_blues, cet_blues_r, cet_bmw, cet_bmw_r, cet_bmy, cet_bmy_r, cet_colorwheel, cet_colorwheel_r, cet_coolwarm, cet_coolwarm_r, cet_cyclic_grey_15_85_c0, cet_cyclic_grey_15_85_c0_r, cet_cyclic_grey_15_85_c0_s25, cet_cyclic_grey_15_85_c0_s25_r, cet_cyclic_mrybm_35_75_c68, cet_cyclic_mrybm_35_75_c68_r, cet_cyclic_mrybm_35_75_c68_s25, cet_cyclic_mrybm_35_75_c68_s25_r, cet_cyclic_mygbm_30_95_c78, cet_cyclic_mygbm_30_95_c78_r, cet_cyclic_mygbm_30_95_c78_s25, cet_cyclic_mygbm_30_95_c78_s25_r, cet_cyclic_wrwbw_40_90_c42, cet_cyclic_wrwbw_40_90_c42_r, cet_cyclic_wrwbw_40_90_c42_s25, cet_cyclic_wrwbw_40_90_c42_s25_r, cet_dimgray, cet_dimgray_r, cet_diverging_bkr_55_10_c35, cet_diverging_bkr_55_10_c35_r, cet_diverging_bky_60_10_c30, cet_diverging_bky_60_10_c30_r, cet_diverging_bwr_40_95_c42, cet_diverging_bwr_40_95_c42_r, cet_diverging_bwr_55_98_c37, cet_diverging_bwr_55_98_c37_r, cet_diverging_cwm_80_100_c22, cet_diverging_cwm_80_100_c22_r, cet_diverging_gkr_60_10_c40, cet_diverging_gkr_60_10_c40_r, cet_diverging_gwr_55_95_c38, cet_diverging_gwr_55_95_c38_r, cet_diverging_gwv_55_95_c39, cet_diverging_gwv_55_95_c39_r, cet_diverging_isoluminant_cjm_75_c23, cet_diverging_isoluminant_cjm_75_c23_r, cet_diverging_isoluminant_cjm_75_c24, cet_diverging_isoluminant_cjm_75_c24_r, cet_diverging_isoluminant_cjo_70_c25, cet_diverging_isoluminant_cjo_70_c25_r, cet_diverging_linear_bjr_30_55_c53, cet_diverging_linear_bjr_30_55_c53_r, cet_diverging_linear_bjy_30_90_c45, cet_diverging_linear_bjy_30_90_c45_r, cet_diverging_rainbow_bgymr_45_85_c67, cet_diverging_rainbow_bgymr_45_85_c67_r, cet_fire, cet_fire_r, cet_gray, cet_gray_r, cet_gwv, cet_gwv_r, cet_isolum, cet_isolum_r, cet_isoluminant_cgo_70_c39, cet_isoluminant_cgo_70_c39_r, cet_isoluminant_cgo_80_c38, cet_isoluminant_cgo_80_c38_r, cet_isoluminant_cm_70_c39, cet_isoluminant_cm_70_c39_r, cet_kb, cet_kb_r, cet_kbc, cet_kbc_r, cet_kg, cet_kg_r, cet_kgy, cet_kgy_r, cet_kr, cet_kr_r, cet_linear_bgy_10_95_c74, cet_linear_bgy_10_95_c74_r, cet_linear_bgyw_15_100_c67, cet_linear_bgyw_15_100_c67_r, cet_linear_bgyw_15_100_c68, cet_linear_bgyw_15_100_c68_r, cet_linear_blue_5_95_c73, cet_linear_blue_5_95_c73_r, cet_linear_blue_95_50_c20, cet_linear_blue_95_50_c20_r, cet_linear_bmw_5_95_c86, cet_linear_bmw_5_95_c86_r, cet_linear_bmw_5_95_c89, cet_linear_bmw_5_95_c89_r, cet_linear_bmy_10_95_c71, cet_linear_bmy_10_95_c71_r, cet_linear_bmy_10_95_c78, cet_linear_bmy_10_95_c78_r, cet_linear_gow_60_85_c27, cet_linear_gow_60_85_c27_r, cet_linear_gow_65_90_c35, cet_linear_gow_65_90_c35_r, cet_linear_green_5_95_c69, cet_linear_green_5_95_c69_r, cet_linear_grey_0_100_c0, cet_linear_grey_0_100_c0_r, cet_linear_grey_10_95_c0, cet_linear_grey_10_95_c0_r, cet_linear_kry_5_95_c72, cet_linear_kry_5_95_c72_r, cet_linear_kry_5_98_c75, cet_linear_kry_5_98_c75_r, cet_linear_kryw_0_100_c71, cet_linear_kryw_0_100_c71_r, cet_linear_kryw_5_100_c64, cet_linear_kryw_5_100_c64_r, cet_linear_kryw_5_100_c67, cet_linear_kryw_5_100_c67_r, cet_linear_ternary_blue_0_44_c57, cet_linear_ternary_blue_0_44_c57_r, cet_linear_ternary_green_0_46_c42, cet_linear_ternary_green_0_46_c42_r, cet_linear_ternary_red_0_50_c52, cet_linear_ternary_red_0_50_c52_r, cet_rainbow, cet_rainbow_bgyr_35_85_c72, cet_rainbow_bgyr_35_85_c72_r, cet_rainbow_bgyr_35_85_c73, cet_rainbow_bgyr_35_85_c73_r, cet_rainbow_bgyrm_35_85_c69, cet_rainbow_bgyrm_35_85_c69_r, cet_rainbow_bgyrm_35_85_c71, cet_rainbow_bgyrm_35_85_c71_r, cet_rainbow_r, cool, cool_r, coolwarm, coolwarm_r, copper, copper_r, cubehelix, cubehelix_r, flag, flag_r, gist_earth, gist_earth_r, gist_gray, gist_gray_r, gist_heat, gist_heat_r, gist_ncar, gist_ncar_r, gist_rainbow, gist_rainbow_r, gist_stern, gist_stern_r, gist_yarg, gist_yarg_r, gnuplot, gnuplot2, gnuplot2_r, gnuplot_r, gray, gray_r, hot, hot_r, hsv, hsv_r, inferno, inferno_r, jet, jet_r, magma, magma_r, nipy_spectral, nipy_spectral_r, ocean, ocean_r, pink, pink_r, plasma, plasma_r, prism, prism_r, rainbow, rainbow_r, seismic, seismic_r, spectral, spectral_r, spring, spring_r, summer, summer_r, tab10, tab10_r, tab20, tab20_r, tab20b, tab20b_r, tab20c, tab20c_r, terrain, terrain_r, viridis, viridis_r, winter, winter_r