how to see if a rgb color is too light

Question

I have an aplication in which the customer chooses a color. I can't let this color be too light. Is there a way to see this, to prevent the customer from chosing a color that is too light?

Thank you a lot!

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too light in the case is a color almost white....i have a web site with a white background and the user can choose a color through a jquery plugin.

I want to allow the user to choose the color he wants, but cant be too light.

Answer 1

If contrast is what you are looking for then check out this article.

They show a function like this to choose text color based on any arbitrary color:

function isTooLightYIQ(hexcolor){
  var r = parseInt(hexcolor.substr(0,2),16);
  var g = parseInt(hexcolor.substr(2,2),16);
  var b = parseInt(hexcolor.substr(4,2),16);
  var yiq = ((r*299)+(g*587)+(b*114))/1000;
  return yiq >= 128;
}

// usage:
element.style.color = isTooLightYIQ('ff0045') ? '#000' : '#fff';

The above function will return true if the color is too light for white text to be readable on top of this color.