Your color is messed up - you need to divide by 255 to get the color values in the range of 0-1. This works fine:
plot3(1, 2, 3, 'x', 'Color', [255, 153, 51] / 255, 'MarkerSize', 30, 'LineWidth', 3);
grid on;
Find the treasures in MATLAB Central and discover how the community can help you!
Start Hunting!