Mandatory fields in selenium webdriver not changing the color of the dropdown from red to blue once value is selected?

I am new to Selenium Webdriver , I have an application build in angular 2 and trying to select values in drop down which are mandatory.

1) Select a value from a dropdown; initially the dropdown is red in color (red is the requirement).

2) As soon as a value is selected from the dropdown the border color of the dropdown should be blue.

I am able to select values successfully from dropdown however the color is still remaining red and not changing to blue please suggest why?

Select Speciality_dd = new Select(driver.findElement(By.name(“boardCertificationSpeciality0”)));
Speciality_dd.selectByVisibleText(“Addiction Medicine”);
Thread.sleep(1000);

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