diff --git a/gui/core/colors.py b/gui/core/colors.py
index a6c3699..d1efbf2 100644
--- a/gui/core/colors.py
+++ b/gui/core/colors.py
@@ -3,6 +3,9 @@
 # Released under the MIT License (MIT). See LICENSE.
 # Copyright (c) 2020 Peter Hinch
 
+# See color names and hexadecimal codes at
+# https://en.wikipedia.org/wiki/Web_colors#Basic_colors
+
 from color_setup import SSD
 
 # Code can be portable between 4-bit and other drivers by calling create_color
@@ -11,23 +14,26 @@ def create_color(idx, r, g, b):
     if not hasattr(SSD, 'lut'):
         return c
     if not 0 <= idx <= 15:
-        raise ValueError('Color nos must be 0..15')
+        raise ValueError('Color numbers must be 0..15')
     x = idx << 1
     SSD.lut[x] = c & 0xff
     SSD.lut[x + 1] = c >> 8
     return idx
 
+# Colors must be safe to convert to RGB565 and RGB444.
+# It is recommended to use numbers 10, 11, 12 to color redefinition by a user.
+
 if hasattr(SSD, 'lut'):  # Colors defined by LUT
     BLACK = create_color(0, 0, 0, 0)
     GREEN = create_color(1, 0, 255, 0)
     RED = create_color(2, 255, 0, 0)
-    LIGHTRED = create_color(3, 140, 0, 0)
+    LIGHTRED = create_color(3, 140, 0, 0)  # actually darker than red !!!
     BLUE = create_color(4, 0, 0, 255)
     YELLOW = create_color(5, 255, 255, 0)
     GREY = create_color(6, 100, 100, 100)
     MAGENTA = create_color(7, 255, 0, 255)
     CYAN = create_color(8, 0, 255, 255)
-    LIGHTGREEN = create_color(9, 0, 100, 0)
+    LIGHTGREEN = create_color(9, 0, 100, 0)  # actually darker than green !!!
     DARKGREEN = create_color(10, 0, 80, 0)
     DARKBLUE = create_color(11, 0, 0, 90)
     # 12, 13, 14 free for user definition
@@ -36,13 +42,13 @@ else:
     BLACK = SSD.rgb(0, 0, 0)
     GREEN = SSD.rgb(0, 255, 0)
     RED = SSD.rgb(255, 0, 0)
-    LIGHTRED = SSD.rgb(140, 0, 0)
+    LIGHTRED = SSD.rgb(140, 0, 0)  # actually darker than red !!!
     BLUE = SSD.rgb(0, 0, 255)
     YELLOW = SSD.rgb(255, 255, 0)
     GREY = SSD.rgb(100, 100, 100)
     MAGENTA = SSD.rgb(255, 0, 255)
     CYAN = SSD.rgb(0, 255, 255)
-    LIGHTGREEN = SSD.rgb(0, 100, 0)
+    LIGHTGREEN = SSD.rgb(0, 100, 0)  # actually darker than green !!!
     DARKGREEN = SSD.rgb(0, 80, 0)
     DARKBLUE = SSD.rgb(0, 0, 90)
     WHITE = SSD.rgb(255, 255, 255)
diff --git a/gui/demos/check_colors.py b/gui/demos/check_colors.py
new file mode 100644
index 0000000..2c5a546
--- /dev/null
+++ b/gui/demos/check_colors.py
@@ -0,0 +1,33 @@
+# check_colors.py Test/demo program for any nano-gui displays
+
+# Released under the MIT License (MIT). See LICENSE.
+# Copyright (c) 2021 Ihor Nehrutsa
+
+from color_setup import *  # Create a display instance
+from gui.core.colors import *
+from gui.core.nanogui import refresh
+
+refresh(ssd, clear=True)  # Initialise and clear display.
+# Uncomment for ePaper displays
+# ssd.wait_until_ready()
+# ssd.fill(0)
+
+# Fill the display with stripes of all colors
+COLORS = 16
+dh = ssd.height // COLORS
+for c in range(0, COLORS):
+    h = dh * c
+    ssd.fill_rect(0, h, ssd.width, h + dh, c)
+if dh * COLORS < ssd.height:
+    ssd.fill_rect(0, dh * COLORS, ssd.width, ssd.height - dh * COLORS, BLACK)  # Fill in the remaining blank area at the bottom
+
+# half frame at the top of the screen
+ssd.line(0, 0, ssd.width - 1, 0, WHITE)  # top line from left to right
+ssd.line(0, 0, 0, ssd.height // 2, WHITE)  # left line from top to middle
+ssd.line(ssd.width - 1, 0, ssd.width - 1, ssd.height // 2, WHITE)  # right line from top to middle
+# half frame at the bottom of the screen
+ssd.line(0, ssd.height//2, 0, ssd.height-1, MAGENTA)  # left line from middle to bottom
+ssd.line(ssd.width - 1, ssd.height//2, ssd.width - 1, ssd.height-1, MAGENTA)  # right line from middle to bottom
+ssd.line(0, ssd.height-1, ssd.width - 1, ssd.height-1, MAGENTA)  #  bottom line from left to right
+
+ssd.show()