how to get gray color

hi, how to get a gray color, I use its value but it gives me black color

 grayImg = insertShape(I,'line',[270 20 30 200],'LineWidth',10,'Color', [0.75 0.75 0.75] ); figure,imshow(grayImg);

Answer 1

[Image Analyst]

Try using gray levels instead of the 0-1 range. (It's inconsistent, I know)

grayImage = imread('cameraman.tif');
subplot(2, 2, 1);
imshow(grayImage);
title('Original Image', 'fontSize', fontSize);
drawnow;

grayImg = insertShape(grayImage, 'line', [270 20 30 200], ...
  'LineWidth', 10, 'Color', [0.75 0.75 0.75]*255 ); 
subplot(2, 2, 2);
imshow(grayImg);
impixelinfo;