DigitalColor Meter is handy for sampling on-screen colour

Installed with every Mac, DigitalColor Meter gives you accurate readings of on-screen colours: you can inspect individual pixels, and copy and paste RGB values. When used with Safari or Firefox and a great text editor, it’s a lightweight but powerful tool. Here’s an overview…

 

• Find it in /Applications/Utilities/
• For using with HTML and CSS,  set the colour type to “RGB as Hex Value, 8-bit”
• Command+Shift+c to copy the current colour as text – perfect for pasting straight into a .css file, alternatively, click and drag from the swatch area to copy the current colour as text (switch this on in preferences first)
• Command+Shift+h to hold the current colour
• Set the magnification factor to maximum and the aperture size to minimum for pixel-perfect sampling. Handy for ‘borrowing’ font colours from other sites!
• Reduce the magnification factor and increase the aperture size for getting an averaged colour – say, when you’re working with gradients or photos
• When DigitalColor Meter is the active app, you can use the arrow keys to move the aperture in one-pixel increments
• You can also save the current hovered area as a .tiff file, or copy it to the clipboard. 
• Set the window to float and keep it in the bottom right of the screen, so it’s always there at a glance. 

One last point: on Tiger at least, if you switch users to a user who has DigitalColor Meter running it will crash. But that’s an annoyance at worst…