[R] axis() color from 1.5.1 to 1.6.1

[partha_bagchi@hgsi.com]

I see that the definition of axis() has changed from 1.5.1 to 1.6.1 (as 
mentioned in the news file for 1.6.0). Axis now has a color argument to 
change it's color. However, the following command worked in 1.5.1:

> axis(1, at = c(0.1, 0.2, 1, 5, 10), fg= gray(0.7), cex.axis = 0.8, 
col.axis= "red") #plot the axis in gray with annotations in red.

The command no longer works in 1.6.1. I am aware that using a col argument 
in axis would work. However, this does break code written currently (for 
1.5.1) and thus the danger of code being specific to the version of R that 
one is using. 

I am interested in knowing why it does not work.

Thanks,
Partha.