I need to blend a white text on top of a multicolored background and I only want to blend with a particular base color. (in this case it's the orange)
How do I configure blending options to do this?
You would need to use a layer mask that matches the position of the orange color. Attaching this layer mask the the text you want blended would hide/show only the corresponding areas.
If you duplicate the text layer with layer mask (change text color), then invert that layer mask (black where the white was in the first one and vice versa). The two text layers together would give you what you are after.
Alternatively you could simply use an adjustment layer and attach the mask to that instead.