Highlight Row percent change on the day is > x

This depends on how you compute the "percent change on the day".

1. The built in column that displays percent change is based on the previous bar's close to the current price.
2. Some might describe "percent change on the day" as the percent change from today's open to the current price.

Here is the code for the first scenario:

input percentThreshold = 30.0;
plot percentChange = if close[1] > 0 then 100 * (close / close[1] - 1) else 0;
percentChange.AssignValueColor(if percentChange > percentThreshold then Color.BLACK else Color.CURRENT);
AssignBackgroundColor(if percentChange > percentThreshold then Color.YELLOW else Color.CURRENT);

And here is the code for the second scenario:

input percentThreshold = 30.0;
plot percentChange = if open > 0 then 100 * (close / open - 1) else 0;
percentChange.AssignValueColor(if percentChange > percentThreshold then Color.BLACK else Color.CURRENT);
AssignBackgroundColor(if percentChange > percentThreshold then Color.YELLOW else Color.CURRENT);

Both of those are applied to a daily time frame to compute the values for the current trading day.

Screenshot below shows the result.