Can you tel me a type of plastic which absorbs maximum amount of UV
light and is NOT black in color. can you also tell me what color will
absorb more UV light. (NOT black)

The information in comment (design of the smoke detector chamber) is useful
(and should be placed in question clarification) but question is still very
ambiguous. Neverthless, I hope this material will be useful and, at least, 
will allow you to formulate next question or step in more specific manner.

 Most Smoke Detectors rely on ionising  radiation and look like this:
http://www.howstuffworks.com/smoke.htm
I assume you are considering some king of Photoelectric Detectors, which
work like this 
 http://home.howstuffworks.com/smoke1.htm
Some combine both:
http://www.ansul.com/fireprotection/Products/VESDA/f2001183.pdf

In all cases, the air needs to enter inside of the chamber, so you need to
specify the design and also what the plastic properties should be:
be transparent to IR  or to absorb it.
The spectrum needs be better specified. It seems that you are looking for
material transparent in the IR range and having a (what) color in the
visible range - that is being reflecting or scattering in visible.

 Spectrum is shown here:

http://www.abrisa.com/guide/understandinglight/light.spectrum.asp

INFRARED  band is very wide: 0.7-1,000 [µm] - we may not need
transparency in the whole range.

The main points are: It is more complex then 'what plastic'. Optical
properties depend on both chemical composition and on fillers ,
coatings
and dispersed particles and intermediate structure (particle sizes).

Here is example of description of optical properties and databases 
http://www.acdlabs.com/products/spec_lab/exp_spectra/uv_ir/


Practical solution for you issue could be to select material vendor:
 http://www.thomasregisterdirectory.com/plastic_materials/plastic_materials_0055919_10.html

and describe the spectrum you want 
e.g. (transparent in range 10 to 100 micrometers and appearing pink in
visible) then ask for recommendation (of material and surface
treatment)

SEARCH TERM would be:  plastic material vendor, optical properties,
                        optical properties of polymers, database

Another approach may be to keep current product and just seek coating
(paint) which will not impact function but just change the appearance.

I hope this description was useful

Hedgie

Check out companies that sell commercial solar panels, try to find out
what plastics they use. Also blue is a substitude for black, however
in most cases people use a silver codet plastic to reflect the light
to a certain area which generates 3 times the amout of heat that one
would normally collect.

What about same question for infra red light.
Is blue also a subsitute for black here/

Bill

Not sure if you mean visually opaque or transparent.

Most plastics which transmit visible but absorb UV are colourless.
Absorption of UV is achieved with additives. Same is true of IR. There
are few native coloured transparent plastics -- cellulose acetate
(yellow) being the most common.

The colour (eg blue) has no simple significance upon UV absorption or
lack of it, though many additives are designed for bandpass so one
would tend to find that longer wavelength colours would also absorb
near UV. No guarantee though.

If you mean visibly opaque, the plastic can be any colour you like,
usually by additives. Additional UV absorption is again usually
imparted by additives, so colour is no indicator of UV properties.

Best

I am extremly sorry i should have said IR and not UV. The main purpose
of the appliction is the smoke detector chamber. All detector chambers
are black and i am interested in designing a non black chamber. The
reason for this is that part of the moulding is exposes and the black
ring does not look good.

The nanoshell materials made by the Halas Lab at Rice have pretty big
NIR absorbances. One should be able to imbed them in a plastic matrix.

http://www-ece.rice.edu/~halas/

More conventionally,

http://www.azom.com/news.asp?newsID=1957
Lumogen® IR 788 and Lumogen® IR 765 in contrast are thermostable,
highly transparent NIR selective absorbers, from BASF.