I want to create text with gradient colors like a rainbow

I omitted saying you may need to use a drawing application to create the shapes in the first place. In this case converting your text to outlines (simple vector path definitions not a text function which draws the paths in postscript language according to your characters and a font file). In your case wanting 'cutouts' as svg2key calls compound paths you'll probably need a drawing application. If you download svg2key the Manual PDF discusses various applications and there are many others out there look at the download section of Apple Support.

From the svg2key Manual:
"• Inkscape - My favorite program for creating vector graphics. Inkscape is open source
(i.e. free) and since Inkscape is strictly an SVG editor, its output is fairly clean. Please
note that Inkscape runs in the X11 environment, so you will need to install the
developer tools from your Mac OS X installation DVD or CD to run it. Inkscape can be
obtained from http://www.inkscape.org."

"If you have a composite graphic like the molecular diagram shown above-left, svg2key
will preserve the relative positions of each shape in the Keynote file. However if you
intend for the collection of shapes to remain as a whole, as with the stick figure shown
above-right, you are better off joining each path before saving the SVG file (by selecting
Path> Union in Inkscape). As of this writing, Keynote will not resize grouped objects, so
by merging the paths you can adjust the size, fill color and line thickness of the entire
shape in Keynote."

All drawing programs I use can make compound shapes. Compound shapes essentially are sapes or regions defined by more than one closed path. Take the letter "O". This has an inner path and an outer path. The outer path inthis case describes the included region and the inner path the excluded region. You can see why they get called 'cutout' or 'cookie cutter' shapes now. Most programs just have an odds and evens overlapping approach, subtracting and adding from the defined region with each overlapping path making up the compound path.

Another definition is clockwise and anti-clockwise path directions assigned to included/excluded regions respectively ( hope I got that the right way around 😉 ).

Making a compound shape (with or without cut-outs) does the job of 'joining' that Brian quite rightly drew your attention to. AFASK you can't convert text to an outline in Keynote or Preview.

You can use you text to mask a "rainbow" image. Need to convert text to a shape or vector path (svg2key is free). Rainbow can be a photo or something from a drawing/painting application... there's a few hundred out there.

actually, if you use svg2key, make the whole line of text a joined or compound object before exporting to the SVG. That will make it act like ONE object. Then convert it to Keynote and then you can apply the new advanced gradient fill to it, that should let you make all sorts of pretty color bands inside the text 🙂

Photoshop Elements? Maybe Acorn or Pixelmator? Demos for all three can be downloaded.

Brian Peat wrote:
then you can apply the new advanced gradient fill

Holy cow, I missed an incredibly cool new feature of KN '09! Thanks, Brian!

Just only discovered the new gradient myself the other night. Where was it hiding? Nice point about compound paths Brian, they can really confuse the [novice] illustrator.