The person who is righteous and fears the day of Judgement, Is honest and has good character, his character is manifest from the radiance on his face. Likewise, can be said for a person who is sinful. His face lacks radiance and Noor.
When a person is a child and is too innocent to be sinful, he has a beautiful radiating and bright face. As a person gets older and if he/she leads a sinful life, the Noor of the face is replaced by an ugly face. What is internal becomes apparent on the outside.
Likewise, if a person leads a righteous life, the person will have a bright face.
It has been narrated that Ibn Abbaas (Radiyallaahu anhu) said:
"Indeed righteousness illuminates the heart, radiates the face, strengthens the body, increases provision, and produces a love in the hearts of the creation for that person. Whereas sinfulness darkens the heart, greys the face, weakens the body, and produces hatred in the hearts of the creation for that person."
It is very important to strengthen one's character and morals as an individual and as a community as a whole. One must abstain from sinning, be it a minor or major and always keep repenting to Allah Azzawajal for the intentional as well as unintentional sins.
It is possible that a person may not intentionally lie, he may even be a person who makes a great effort in ibaadah and has zuhd (abstains from pleasures of this life that are lawful). However, he has false, incorrect ‘aqeedah regarding either Allah, His deen or His Messenger (sallallaahu ‘alayhi wa sallam) or His righteous servants. And what is on the inside affects what is on the outside. Thus, this false, incorrect ‘aqeedah that he thought was true and correct reflects on his face, and his face would be dark in accordance with the level of falsehood he possesses.
As it has been narrated that ‘Uthmaan ibn Affaan (radiyallaahu ‘anhu) said:
No one ever hides evil within themselves except that Allaah makes it manifest from his facial outlook and the statements his tongues utter.
One must always keep in check with his Iman, make righteous friends who remind one of Allah taala often.
On the day of judgment, this would be very clear as Allah says: And on the Day of Resurrection you will see those who lied against Allaah their faces will be black. Is there not in Hell an abode for the arrogant ones? [Soorat uz-Zumar, 39:60]
He ta’ala also said: On the Day when some faces will become white and some faces will become black; as for those whose faces will become dark (to them will be said): ‘Did you reject Faith after accepting it? Then taste the torment for rejecting Faith. [Soorah Aali-Imraan, 3:106]
It is clear from these verses that the faces of sinful will be void of any radiance or Noor and the wrath of Allah is to befall them, for them is the hellfire. May Allah protect us. Ibn Abbaas and others have said regarding the verse above that: The bright faces will be ahlus-sunnah, and dark faces will be the people of Innovation and division. [Aj-jawaab as-saheeh Vol.4, pg. 306-307]