[Genome] Custom Tracks

[Peter Scacheri]

I'm trying to add a custom track with P-value scores.  How do I 
display the track so that the scores are represented in different 
shades of grey, ie., the higher the score, the darker the color. 
Here is an example of my input file.

track name=test
chr1	147973262	147973312	0.372351348
chr1	147973300	147973350	0.372351348
chr1	147973338	147973388	0.353911558
chr1	147973376	147973426	0.335036585
chr1	147973414	147973464	0.315663303
chr1	147973452	147973502	0.29571216
chr1	147973490	147973540	0.275080532
chr1	147973528	147973578	0.253632178
chr1	147974174	147974224	1.725645723
chr1	147974212	147974262	1.725645723
chr1	147974858	147974908	0.08374733
chr1	147975124	147975174	3.82209489
chr1	147975162	147975212	3.409069051
chr1	147975200	147975250	3.064172447
chr1	147975238	147975288	2.77180428
chr1	147975276	147975326	2.520802915
chr1	147975314	147975364	2.302969809
chr1	147975352	147975402	2.112146061
chr1	147975390	147975440	2.112146061
chr1	147975428	147975478	0.948169009
chr1	147975466	147975516	0.178606953
chr1	147975504	147975554	0.372351348
chr1	147975542	147975592	0.372351348
chr1	147975580	147975630	0.178606953
chr1	147975618	147975668	0.178606953
chr1	147975656	147975706	0.178606953


Thank you!
Peter