Amazing Amethyst 
When I first started to use this colour, it was not at the top of my list. I thought that sometimes the colour looked weak when I was writing with it. But when I went back and looked at notes I had taken using this colour I noticed the ink is darker as it dries. Also, the overall colour tone was much more pleasant to the eye than I had first thought.
Yes, you could use this ink for business purposes. Some purples can bed a bit harsh. Not Amazing Amethyst.
The flow of the ink is good. So far it has been used primarily in my OMAS 360, the classic, with a Broad nib and a Montblanc 146 with a Stubg nib. (Yes I do own Montblanc pens!) Both of those pens leave a good solid line of ink on the page. The ink was totally dry on the paper within five seconds. But remember, the time to dry will depend on the paper you use.
No real shadding to speak of in terms of colour variance. As you can see by the sample to the right, there is some difference in terms of the amount of ink a Broad nib places on the paper on some of my strokes.
The colour is consistent through the entire stroke as you form your letters.
The ink dries in a good reasonable time. I had no problem with smearing.
The ink colour sample that is on the Diamine website is not the best representation of the colour. If you look at the scan of my writing to the left, and then the colour swatch below you will see the difference. I have seen samples of this ink on other web sites and the ink on some seems to be darker than what I have experienced with the bottle I have. All I can say is that the scan I have posted is a true reflection of the colour I have been using.
There is too much blue in the colour swatch and if you look at the writing sample above, there is real purple and less blue to the ink.
Damson
This is an interesting colour, purple with a good mixing of black to give it a very subtle look.
When using for business writing, and going back and looking at a page of meeting notes, the page looks like a black with a undercolour of purple. Most of the pens I used have had broad or stub nibs. The nibs left broad lines of line on the page so there was ample opportunity of tones to show.
The color swatch on the Diamine web site is representative of the colour I found in using the ink.
Imperial Purple
This is a bold,bright purple.
There is a richness to the tone. Despite its bright look, I find it OK for business use as well as personal notes and cards.
Good flow and drying time OK.
Ink colour, in a variety of pens with various nibs is fairly consisent with the colour swatch on the Diamine web site.
Lavender
Here is another very rich, saturated colour in the violet/purple grouping.
Lavender is not as "pastel" as I would have throught, given the name, and the more I used the ink, the more I liked the colour.
The ink performed well in a variety of pens and nibs. With broad nibs there good shading take place on the strokes. It all added to the character of the ink.
The colour swatch on the Diamin web sitre has considerably more blue tones that what I exerienced, regardless the the pen and nib combination.
Majestic Purple
This colour was issued in 2009 and when I had the opportunity to use it, it is one of violet/purple colours that I particuarly liked.
I noticed, however, there is a significant colour shift, depending the the nib style that is used. The sample above is with a Krone Fiction with a broad nib. The Krone nibs are very smooth and the Majestic Purple has good flow. There a more than adequate amount of ink being delivered to the paper.
For example, the ink appears shades darker when I used a Pelikan M1000 Oblique Medium Nib. The M1000 deliver a flood of ink to the paper. The nib is a bit narrower and I was surprised at the difference in colour tone.
The colour swatch from the Diuamine web site turns out to be in the middle of the two tones.
Violet
A softer tone in the violet/purple group.
I have used this for both personal and business writing. My personal preference is the slightly darker and saturated colour tone of Imperial Purple.
The colou swatch on the Diamine web site has considerable more blue ton