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If one site is given an actual White Bar PR0 then it is penalised and there are probably a hundred or more threads on this forum discussing "PR0" if you use the site search facility.
This is totaly different to a greyed out bar which normaly means not yet indexed.
If you do in fact have a "PR0" you may have to consider scrapping that particular domain name because lifting this penalty is unpredictable in timescale. 3 months, 6 months a year, even never. Who knows?
I'm dealing with a related situation. I've found out that a site I just started working with has two additional domains pointed to it. They all return a 200, and all have links to them from one particular site, with the 2 having that as the only link, but the main site having many. It's not quite the same thing, but it still comes down to practices that entail risk, in varying degrees.
In the case I mentioned I believe there could be a penalty down the road and it needs to be remedied ASAP. Too often people do things without realizing the possible implications. In your case, I'd ditch one of those sites, and either stay with just one or make a whole different, unique site with the other, unless it is, in fact, penalized.
As far as how different yours are - differences in color scheme aren't relevant. How similar are they in HTML structure and navigation, and most important, how close is the site content - the text? If they're affiliate sites, do they have the same vendors linked to? Where are there actual elements of similarity, and in what ways are they different?
By the way Marcia do you see any problem with:
myurl.com and myurl.co.uk both pointing to the same server space.
It should be 301, not 302 - there's a difference. jdMorgan explained it in a thread in Webmaster General, and it's words to the wise that should be listened to.
Check out the dynamite mod_rewrite tutorial DaveAtIFG did in our Technology forum. I'm not a tech expert, very far from it, and that's clear as a bell even to me. Also look up 301 redirection and mod_rewrite in the site search.
Thanks for the 20% reminder. I seem to remember that figure, but wasn't sure. It does sound about right. That can be important, especially on product or catalog pages where common navigation is carried across and there isn't much unique on each page text-wise.