Alternate highlighting of duplicate values

Your list of data in column A cell 2 (best sorted so as to group like data)
In C1 enter 0 or leave blank
In B2 =IF(A1=A2,"",1)
In C2 =C1+IF(B2=1,1,0)
Copy these 2 cells down to match col A
Conditional formatting - select row 2 then in rule 1 enter =ISODD($C2) then select required formatting then OK. Copy formatting and apply to rows as required

Nice, I was using something similar for finding amount remaining in a lot after sending, but it never occured to me to use odd even numbers.

This is slightly easier

in B2

if(A1=A2,B1+0,B1+1)

Copy and drag down the collumn

Problem now is that conditional formatting is throwing color all over the place, but ive been having issues with that all day. Maybe try on onother computer tomorrow.

Thanks very much!