I am a fresher 
just answering you through searching the topic

 Alternating row shading can be done in webi thru alternate 
row shading property, but in deski we need to create a 
formulae for fetching the row numbers and creating alerter 
like =even(line number)
then all the even 2,4,6.. will be in one colour
if you write
=odd(line number)
then all the odd lines 1,3,5 will be in different colour
hope it will help you

Alternating row shading can be done in deski.
To show the different color in different row 
Create a New variable.
put the formula
=Mod(Rowindex(),2) in new variable.
click ok.
add this variable in to report
Now create a Alerter and put 1 or 0 and color.
Now you can get the different color in different row.

Let me put this very simple.

1.Create a local variable Evenline with this formula in it
     =Even(LineNumber())
------------------------------
LineNumber() returns the number of current line in the block
Even(LineNumber()) returns 1 for a even lines and returns 0
for odd lines.
---------------------------------
2.Now create a new alerter and go to the conditions tab, and
select the “Evenline” variable in the variable to compare field.
 Value for operator should be equal to1 , 

Go to results box and choose the desired background color
and apply this Alerters to the block.