The nomination changes its role for that stroke
WPBSA’s current rulebook makes a nominated free ball take the value of the ball on; if potted, it is spotted. A colour used as a red therefore does not automatically score its normal colour value.
Reds remain and a free ball is awarded. The player nominates the brown as a red and pots it legally. The score for that nominated ball is one, not four. Its physical colour has stayed brown while its temporary scoring role has changed.
Keep ball identity and ball role apart
A television graphic may continue to show the brown ball icon or display its ordinary value elsewhere. Those presentation choices do not override the nomination. Record what was on and what was nominated before adding points.
The example isolates a single legal nominated pot; it does not combine extra reds, simultaneous pots or every later colour choice into the same calculation. It explains why the referee can return a colour to its spot after only one point has appeared. The return and the scoring amount come from the nominated role, rather than a correction of a wrongly counted ordinary brown.
Questions answered
Does a brown nominated as a red automatically score four?
No; it takes the red’s value.
Why can it return to its spot?
A potted nominated free ball is spotted.
Sources & further reading
Official references for the subjects discussed. Service terms and device software can change.