update colors for colab (#357)

Author: waltsims

examples/us_bmode_linear_transducer/us_bmode_linear_transducer.ipynb

@@ -400,15 +400,14 @@
     "ax = plt.gca()\n",
     "ax.set_ylim(40, 5)\n",
     "plt.subplot(1, 3, 2)\n",
-    "plt.imshow(scan_lines_fund.T, cmap='grey', aspect='auto',  extent=[y_axis[0], y_axis[1], x_axis[1], x_axis[0]],\n",
-    "           )\n",
+    "plt.imshow(scan_lines_fund.T, cmap='gray', aspect='auto',  extent=[y_axis[0], y_axis[1], x_axis[1], x_axis[0]])\n",
     "plt.xlabel('Image width [mm]')\n",
     "plt.title('Fundamental')\n",
     "ax = plt.gca()\n",
     "ax.set_ylim(40, 5)\n",
     "plt.yticks([])\n",
     "plt.subplot(1, 3, 3)\n",
-    "plt.imshow(scan_lines_harm.T, cmap='grey', aspect='auto', extent=[y_axis[0], y_axis[1], x_axis[1], x_axis[0]])\n",
+    "plt.imshow(scan_lines_harm.T, cmap='gray', aspect='auto', extent=[y_axis[0], y_axis[1], x_axis[1], x_axis[0]])\n",
     "plt.yticks([])\n",
     "plt.xlabel('Image width [mm]')\n",
     "plt.title('Harmonic')\n",