Today I am still a big fan of 4001 Royal Blue. I use it in my Pelikan M200 with M400 Fine nib. It flows very well and it does everything I want.
There is one thing I absolutely dislike of it, and that is the color when it is dry. The wet-color is fabulous, and the dry-color is boring. And on some paper it seems to fade even more.
But... writing (and reading back) are two different things for me. The experience while writing with this ink is so good, I can not stop using it. I wished there existed a ink in this color that behaves just as 4001 royal blue and keeps its color when dry.
I have similar feelings about 4001 Königsblau and Waterman ‘Serenity Blue’, and about Parker Quink ‘Washable Blue’ (the nearest British equivalent to 4001 Königsblau) - its feel when writing and quick drying time are great, and I love its colour when wet, but dislike the pale colour it turns to when it is dry.
Of course, I suppose that ease of washing and erasure are the most important features for an ink intended to provide problem-free use by school students.
I found a solution to my problem by buying Parker Quink ‘Blue’ - not ‘Washable Blue’ - and I find that it has the same wet-under-the-nib feel that enables the nib to glide across the page, and that the ink dries quickly on the page too.
It isn’t water-resistant, and I don’t know whether one can use ink eradicators with it, but it does retain the depth of its colour after it dries - so it looks a much deeper and more vibrant hue once dry than do the ‘Washable’ Quink, the ‘Serenity Blue’, or the Pelikan 4001 Königsblau.
I haven’t ever seen it in bottles in shops here in the UK, but the ‘WH Smith’ store in my small town does stock it in cartridges, and of course our online retailers do sell Quink ‘Blue’ in bottles.
I think that it could perhaps suit you too