I've some html text like
<h1>GreenWhiteRed</h1>
Is it SEO friendly to split this text in something like
<h1><span class="green">Green</span><span class="white">White</span><span class="red">Red</span></h1>
Is the text still ranking well and is it interpreted as a single word 'GreenWhiteRed'?
This would greatly harm your SEO ranking. One of the major factors used in calculating pagerank is (probably - nobody knows for sure) a low code to text ratio, in other words, that your code is mostly useful, informative text, rather than a load of tags... even if your extra tags contain relevant information in attributes, unless it's part of a recognised standrad (eg hCards) it will probably not count in your favour.
Most search engine spiders see your site as a text browser would, so they would see the text as GreenWhiteRed still.
Source: http://www.google.com/support/webmasters/bin/answer.py?answer=35769#2
I believe it really matters on the subject of the page. If you have a website about dogs and only dogs then you put in the word cat, nothing will happen. Searches for 'cats' will never reach you. Also with colors, just like Andy said, mean nothing to a spider. The real SEO is what a user would read not see. Try to maintain alt tags and don't overflow the same word.
It does not matter at all. No worries. What wheresrhys said is a common myth.
Start focusing on building strong backlinks. That 's the key to the castle.