Could not agree more with the "get a swatch" suggestion. I loved the colors of the MacDonald of Glencoe modern shown on several websites, but because it was only woven as a standard tartan by Dalgleish I was a bit leary to trust the photo, as I had some custom tartan woven by Dalgleish in a different clan that came out darker and more color "saturated" than I had expected from photos of it. So I ordered a swatch from Scotweb, and indeed the swatch I got was a lot darker and more saturated than what all the online photos showed. So I opted instead for the only other standard stock woven version of that MAcD Glencoe available, a muted House of Edgar version, which matched much better with the color palette (thanks Rex) I was expecting, even though it too was still a wee bit darker than expected.

If you just want a specific tartan and are not too hung up on exactly how the colors appear, you could probably get away without a swatch. If you have any concerns about how the tartan is going to appear, in daylight, fluorescent lighting, etc... GET A SWATCH (of tartan, not one of those plastic Swiss watches).