Colour is widely used in many HTML contexts. We, briefly, introduce the concept of colour in HTML here.
There are two ways to specify colour:
Hexadecimal Colour Representation
Colour for each red, green and blue colour component is represented by a range 0 to 255 decimal (FF hex) where
Thus, we can form:
| Red | Green | Blue | Colour |
| Black | |||
| 255 | 255 | 255 | White |
| 255 | red (full) | ||
| 255 | green (full) | ||
| 255 | blue (full) | ||
| x | x | x | x = 0-255 |
| Shade of grey | |||
| 255 | 255 | Magenta | |
| 255 | 255 | Yellow |
Choosing a predefined colour
You can choose one of 16 predefined colours:
Black, White, Green, Maroon, Olive, Navy, Purple, Gray, Red, Yellow, Blue, Teal, Lime, Aqua, Fuchsia and Silver.
Colour names might be easier to remember but you only have a restricted choice compared with several million possible colours possible with hexadecimal representation.
The quality and choice of colour will depend on the hardware you run the browser on.
To change the background colour you must set the BGCOLOR attribute in the BODY tag.
To specify a hexadecimal number you must put a # before the number and then two hex
digits for each red, green and blue component respectively.
For example:
<BODY BGCOLOR = "#FFFFFF">
gives us a white background.
The CGI script rgb.pl introduced in the last lecture (Section 15) provides an HTML form that helps you compute the value and exact form of output.
RGBtoHex converts standard RGB values (three 0 to 255 ASCII numbers indicating red, green, and blue), into a hexadecimal triplet that can be used for the background and text colors in Netscape 1.1b1 or in any other program that requires colors in this format.
RGB2toHex was written by Eric Murray and Laura Lemay, and is in the public domain. Feel free to install the source for this program on your own system (it requires the perl language and cgi-lib.pl) but please credit us for it (you can use the signature at the bottom of this form).