If you want to get across to your web designer an exact colour that you've spotted and would really like to use, or you have particular colours in your branding that you need to have used consistently in your project, you can use a colour picker tool to get the hex codes for the colours you need.
In web design, we use RGB colours. HTML colour codes are hexadecimal triplets representing the colours red, green, and blue (#RRGGBB). For example, in the colour red, the colour code is #FF0000, which is '255' red, '0' green, and '0' blue.
For example, below shows the hex values for different shades of red.
Some great colour picker tools can be seen below:
Colorzilla (an add on for Firefox)
Happy colour picking!
Please Note: If your website uses gradients (is not a solid colour but made up of lots of different shades) you will need to select hex codes for the separate shades.
Also, neon colours or metallic colours such as gold, silver and bronze are a bit more complex, and would probably be best for your web design company to create for you.