How to write the condition in SSRS for dynamically changing color of the cell based on value

1. Choose the Cell / Row / Column that you want to Change the color dynamically
2. Go to Properties (Hit F4)
3. Select Back Ground Color and Choose Expression
4. In the provided window, Give your Expression based on which the color will change.

Refer This Link for more details

try something like this:

=IIf((Fields!nbday.Value >= 0 and Fields!nbday.Value < 90) ,"#3174c3",IIf((Fields!nbday.Value >= 90 and Fields!nbday.Value < 120),"#02C1D3","No Color"))