The best I can describe the color of the Eco Plum is that it is a magenta-ish color with a bit of pink and purple. The solo pictures make the Eco look more red than it is in real life, regardless of background (and yes, this is with some post-processing already - definitely not my strong suit). And despite using custom white balance with a grey card, the writing mat colors aren’t truly accurate either. This is one reason why ink and pen color photography can be difficult for us amateurs. Of the four photos, I think the closest is the one on the purple mat.
Next, I pulled a bunch of Col-O-Ring swatch cards from my collection and rather than compare the pen to the swatch card, I opted to swatch the inks in a 68 gsm Tomoe River notebook by Odyssey Notebooks. This way I could make sure the ink looks like it would on paper that I use quite often. As with my ink reviews, the swatches were made with a stainless steel Kakimori dip nib in a Kaweco clutch pencil holder.