Reporting Services :: Top 5 And Bottom 3 With Colours In SSRS

I have to display Top 5 values in 'Green' and Bottom 5 in 'Red' out of some data.

Ex: my data is as below 
 
ID Marks
1 98
2 62
3 89
4 97
5 92
6 67

[Code] ....

Expected result is : if the marks are >= 80 then 'Green' (pick only top 5)  if marks are <= 70 then 'Red' (pick bottom 5) else 'Black'

As per my data even though we have values >=80 for more than 5 students display only top 5 in Green and same rule applies for Bottom 5 that means

ID 's : 1 ,3 , 4 , 5, 9 and their marks in Green (pick only Top 5 ) even though we have 6 students who got >=80
ID's : 2 , 6, 16 , 15 and their marks in Red (Bottom 5 but we have only 4 students who got <=70 )