The tie dye design was very popular in the 60's. If you need to design something with this particular retro theme, you can use Photoshop's Filter menu features in conjunction with some editing tools to make a tie dye background.
Make a new file.
Pull out the File menu and click on New. Settings for the dimensions, resolution and background color are entirely up to you. Just make sure the color mode is RGB. There wouldn't be any point in making a grayscale tie dye design.
Fill the canvass with vertical solid-colored bars.
There are a number of ways to do this, through a combination of the Marquee, Shape, and Paint Bucket tools. Just keep in mind that the whole canvass has to be filled up. No background color should show. For the sake of symmetry, you can make vertical bars of similar width. What colors you'll use depends on your tie dye idea. You can go monochromatic, two-tone or use the whole rainbow. In making these vertical bars make sure that they all belong in the same layer.
Transform the vertical bars into a twirl.
Tie dye designs are circular so you will need to rearrange these vertical bars. Pull out the Filter menu, click on Distort, then Polar coordinates, and finally choose Rectangular to Polar. This will transform the sequence of vertical bars into a color wheel. Again pull out the Filter menu, click on Distort, and this time choose Twirl. The colors of the wheel will now spiral towards the hub. Adjust the amount of 'twirling' to your satisfaction. To finalize access the Distort option again under the Filter menu and then choose Spherize,
Add white strokes.
Go to the Layer menu and create a new layer. On this new layer use the Brush tool to create strokes starting from the edge and pointing or leading to the twirl's hub. Your preference will dictate the number and density of strokes. Just make sure they come from all around the canvass' edge. The strokes, although generally linear in orientation, should be taper as they approach the hub and wriggly in shape. You're trying to emulate the real way cloth is tie dyed, where certain portions aren't colored because of the way it is bunched or crumpled.
Blur the colors and strokes.
Pull out Filter once again, click on Blur and choose Guassian blur. Apply this to the white strokes layer to soften the strokes' edges. Shift to the color twirl layer and blend the separate colors through the Blur option under the Filter menu, but this time use Radial Blur instead of Guassian. To finally blend the white strokes layer with the color twirl layer, set the Layer Type of the former to Overlay. This is done through the Layer menu.
Remember to complete each editing or transformation step before you proceed to the next one to reduce the number of times you'll need to undo modifications when something doesn't come out right. It would also help to take note of the settings you apply in the options menus and dialog boxes, so you can easily repeat the process and improve it in case you need to make a similar design in the future.