For this experiment I'm using another color from ArtStuff.com.  This is the #641 Brown color in their list of cement colorants.  It mixed up very similar to the black colorant.  You can order either 1 lb or 5 lb batches of this color.  I got the 1 lb box because I wasn't sure how much would be needed (this was ordered at the same time as the black colorant was) and I didn't want to get stuck with a bunch of colorant if it didn't work out the way I hoped.  I shouldn't have worried.

For these tests I used the same method as I used on the black experiments.  I put close to 40 grams of plaster in a cup then measured out a set percentage of that weight of colorant and added it to the cup with the plaster.  I did lower the water I used for this experiment to 35 grams of water from 45 grams of water.  45 grams of water was way too much water and made the plaster too thin for casting in Hirst Arts molds so I reduced the water to closer to what I normally use for casting.  Notice that the percentages don't come out exactly at the listed percent.  For example the 1% test comes out to be 0.9933% instead of a true 1%.  This is due to the precision of my scale only being 0.01 grams so I am unable to get the exact 0.4027 grams of colorant required.  Technically the amount of colorant could be anything in the 0.40XX range of weights.  I'm not sure whether it rounds a weight up to the nearest 0.1 gram or simply drops the extra number.  Due to this inherent error no two mixes of colorant and plaster will be exactly the same shade.  They should be very close however and I didn't consider this margin of error to be significant.

Stats	Notes	Picture
10% 40.16g plaster 4.01g color	I did the 10% mostly because I had done a 10% test on the last experiment and wanted to reproduce the original experiment as closely as possible.  The result looks more like a rust color to me and it too dark.
2% 40.03g plaster 0.80g color	2% looks pretty good.  It could be used for a dirt colored plaster.  This would be handy for pieces like my Modular Trench system that is mostly dirt.
1% 40.27g plaster 0.40g color	A 1% mix would work fairly well as dirt but isn't as dark as the 2%.  It could work good for brown stone buildings and is really a nice color.
0.9% 40.03g plaster 0.36g color	This color seems to be too much in the middle for me.  It's too dark to make effective wood colors but too light to work for dirt.  I suppose it could work for some dirt and some wood but I probably won't use it much.
0.8% 40.11g plaster 0.32g color	This color is a light brown color and would be great for wooden barrels and planks.
0.7% 40.10g plaster 0.28g color	This would also be good for a wood color, but is a little light for my tastes.
0.6% 40.17g plaster 0.24g color	This is probably too light for wood, but would work fine for some kinds of stone.
0.5% 40.42g plaster 0.20g color	Getting better but still too light for me.
0.4% 40.22g plaster 0.16g color	Darker but still pretty light.
0.3% 40.16g plaster 0.12g color	You'll notice that this color seems lighter than the 0.2% picture below.  This isn't just the pictures the actual sample is lighter than the 0.2% one.  The only thing I can think of is that when I was measuring these two samples I somehow ended up with less colorant in this one than I thought I did.  This could be for several reason including not hitting the side of the cup I used to measure the color in.  It doesn't really matter since this color is way to light to be of any use to me.
0.2% 40.19g plaster 0.08g color	As with the 0.3% I don't know why this ended up darker than the supposed higher concentration.  It's still too light to be of much use to me.
0.1% 40.30g plaster 0.04g color	You can barely tell there's some color in this one.  It's a little brown but not much.

Finally a shot of all the experiments together to compare the colors.

From right to left:
Bottom Row: 0.1%, 0.2%, 0.3%, 0.4%
Second Row: 0.5%, 0.6%, 0.7%, 0.8%
Top Row: 0.9%, 1%, 2%, 10%

Conclusions
This colorant took a lot more colored powder to get a darker shade than the black did.  This color brown is good for dirt and wood colors.  I was hoping it would have a mix that would be good for stone buildings, kind of a buff color.  I suppose I'll find something that will work with another color.  I'm going to go with 2% for a dirt color and 0.9% for wood like barrels and the wooden plank mold.  Just because I plan on using these doesn't mean that there aren't plenty of applications for the other mixes.  I'm sure from time to time I'll be making some special batches of some of the other colors for specific projects.  I am only going to make large 15-20 lb buckets of the 2% and the 0.9%.

Plaster Colorant Experiment Black