I am using this expression in Background color for Volume Expression. So if the volume is greater than vPlus value, then it will show those dots as green color in the chart.
But the Timeframe and Agg_Period fields are not getting excluded in the expression, if we select these two field values in a listbox, then the green color is changing to normal line color.
Have you double checked the exact spelling of your field names in the set expression (your sample expression differs from you stated as field names)? Field names are case sensitive and you need to put in field names only, no labels etc.
Then, what is the definition of vPlus resp. vMinus variable?
It would probably make things easier if you could upload a small sample file that demonstrate your issue.