I believe this is the formula you want in the conditional column:
=IF(EAC1 < BL1, "One", IF(AND(EAC1 >= BL1, EAC1 <= [BL+5%]1), "Two", "Three"))
And then you can conditionally format off of that using the conditional formatting in the leftmost pane. See example below.
https://app.smartsheet.com/b/publish?EQBCT=34a5e4505a674959af55e81ee15faea2