Replacing one word for entire site depending on the URL.
I have two domains. I'd like to replace a word depending on the URL the user has typed in.
Original site is all about red pens. Well I want to make another domain that is bluepens.com, but when they enter in bluepens.com it uses the same pages from red pens except wherever the word 'red' is found it is changed to blue pens making it a whole new site.
I know I can use str_replace() for certain instances, but how would you do it for an entire website using the url?