I love all the comments...no ones sitting on the fence here.
...I already have a loose covered sofa,and have never seen taking the covers off / putting them back on to be a problem. But-its green so does not show dirt so much. It DOES show all the pet hair though. :-(
As for dying the white if it turns out to be a problem-that is already on the '+' side of the list.
What started me thinking this way was this-from IKEA.
http://www.ikea.com/gb/en/catalog/products/S19902387/#/S39875849
Its so damn cheap in the white- add another £200 if a colour is wanted. My budget is really tight at the moment, so even if the white is temporary,I can get new covers not too far in the future. Also-ikea sofas come with a TEN year guarantee.
My other choice is sofasofa...
http://www.sofasofa.co.uk/p/KBAN3/colour/bagr/Banbury-3-Seater-Sofa
But some reviews are quite negative.