When designing elements for your webpage, you will often be called upon to specify a color. For example, the code for a span shown below specifies that the color of the text within the span will be yellow.


<span style="color:yellow;">Text</span>


Colors can be specified according to their names, for example "yellow", "green", or "blue". In many cases, these simple color names will work. But what if you want to specify a more sophisticated color like "cornflowerblue"? A particular browser may not recognize a particular color name. It's more reliable to specify colors with an "RGB triplet".


An RGB triplet specifies a color based upon the amounts of red, green, and blue, on a scale from 0 to 255, required to create the color. For example, to create the color cornflowerblue you need red=100, green=149, and blue=237. We could then specify the color of the text within a span using the rgb function as shown below.


<span style="color:rgb(100,149,237);">Text</span>


This will work fine with style notation, but what if you want to use straight html. Html doesn't recognize the rgb function. In that case, you can specify color using "hexadecimal" notation. Whereas the decimal numbering system uses the characters 0 through 9 to get 10 values, the hexadecimal numbering system uses the characters 0 through f to get 16 values. (After 9 the characters a, b, c, d, e and f are used, as shown below.)


Decimal Hexidecimal Equivilants

dec hex


0 = 0


1 = 1


2 = 2


3 = 3


4 = 4


5 = 5


6 = 6


7 = 7


8 = 8


9 = 9


10 = A


11 = B


12 = C


13 = D


14 = E


15 = F

On first appearance, this looks pretty simple but you need two hexadecimal characters to represent all decimal values from 0 to 255. When you increment decimal 9 by 1, you change the 9 to 0 and put 1 in the ten's place. When you increment hexidecimal F by one, you change the F to 0 and put 1 in the "sixteens" place. Sometimes it's not easy to convert between decimal and hexadecimal in your head.


RGB Triplet for Cornflowerblue

color   dec   hex


red     100    64 


green   149    95


blue    237    ED

We could then specify the color of text within a span using the hexadecimal notation as shown below.


<span style="color:#6495ed;">Text</span>


Note that when we indicate the use of hexadecimal notation by placing a pound (#) sign in front of the number, and we don't use commas to separate the color components.


If it's not easy to convert between decimal and hexadecimal in your head, then how do you do it? You can use a calculator that has a decimal to hexadecimal coversion function, or you can learn to think in hexadecimal. For example, what's the next number after CE? That would be CF. what's the next number after CF? That would be D0. Which hexadecimal number is higher 99 or B2? B2 would be higher than 99. It gets easier with experience.


Here's Java Script code for a simple decimal to hexidecimal color converter

function convert(decvalue)


{


var num = parseInt(decvalue);


if(num >= 0 && num < 256)


{


var hexnum = num.toString(16);


alert("#" + hexnum);


}


else {alert("Error!");}


}

It's important to use hexadecimal notation to specify colors when you use DHTML with visual effects, because to create a dynamic color change you have to increment or add a value to a color. The vast amount of color specification on webpages is in hexadecimal notation, so it would be wise to become familiar with it.


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