Okay, first open up Paint. Then you click on the tab named Image and click on attributes.
Got it? Okay then type in for the width, 100 and height 500. Make sure that it's in Pixels and click OK.
Simple right? Okay, next you'll click on the line tool and draw a diagonal line at the top. Color it, let's say, red or any color. Make sure that the line connects from both side, otherwise when you go to fill it in, it'll fill in the whole picture.
Okay, do the exact same thing, but with a different color. I used the color orange but you can use any color you'd like.
And again but with a different color. Also, space them out a little unless you only want so many colors in your rainbow.
Wow, I sound a little repetitive don't I? Okay add as many colors as you'd like, I'll be doing a simple rainbow so I'll have about six colors :)
And add another color...
Do the last color.
Now the fun begins :) Okay go to the Image tab and then go down to Resize/Skew...
Make sure that the Horizontal is 1 and the Vertical 100. Click OK.
Make sure that your picture is that thin. It's hard to see a little so I circled it :)
Go to Image and go down to Resize/Skew...
Okay instead of changing the Horizontal to 1 change to 500 it only goes up to 500.