Hi.
I think I may have a bug.
I want my particles to be Yellowish, so I picked Yellow in the override color, ok.
I enabled Use Emission and Use Absortion, and I got what you can see in the picture “Enabled_Yelow_Color.jpg”.
if I disable the absortion I get what you can see in the picture “Disabled_Yellow_Color.jpg” which is correct.
Then I though that the color i get with the Absortion enabled and the color in yellow is similar to the opposite color in the color wheel, so I tried tu put a blueish color in the color wheel, and voile, I got my yellow color.
You can see the results in the picture “Enabled_Blue_Color.jpg”
As you can see I have my yellow color, but if I disable the Absortion I get what you can see in the picture “Disabled_Blue_Color.jpg”
You can see the color wheel in the pictures “Disabled_Blue_Color_Wheel.jpg” and “Disabled_Yellow_Color_Wheel.jpg”
Hope this helps (or maybe i’m wrong and it’s some parameter i’m not correctly configuring).
Cheers.
You will need to use “Override Absorption” and specify an Absorption color if you are going to enable “Use Absorption” (unless of course your particles already have an “Absorption” channel).
The absorption section of this document might help: thinkboxsoftware.com/krak-shading/
It is written for the 3dsmax version, but the controls should be the same in Maya.
There may be a bug somewhere here, so I will look into this further.
This effect is expected if somewhat unfortunate.
There are 3 main quantities that Krakatoa uses, and 1 derived one. They are Color, Emission, Absorption and Extinction respectively. Emission is straightforward, and Color is usually easy to understand but Absorption is handled kind of unfortunately. Extinction can be thought of as the inverted shadow color (ie. what is subtracted from light as it passes through the particles). When “Use Absorption” is disabled the Extinction value is considered to be white (ie. [1,1,1]) no matter what the Color value is. When “Use Absorption” is on, the Extinction values is the sum of Color and Absorption. When particles have not been assigned an Absorption value (via the .prt file or from the global override, for example) the Extinction will be equal to the Color meaning that light passing through particles will remove the same color/amount of light as is reflected back towards the camera. The end effect in that situation is that the bulk of your particles will render bizarrely since the dominant color frequency will be quickly removed from a light ray and the interior particles will reflect the less dominant color frequencies. In your case when “Use Absorption” is on you are seeing a very thin band of the expect color at the very edges and the bulk of your particles are reflecting the modified light.
In summary: Absorption is a weird quantity and I wish we directly specified Extinction.
That being said, you will want to set the Absorption value per-particle (probably with the global override) if you have “Use Absorption” enabled.
Thanks for the explanation Conrad and Darcy 
Cheers.