How do biblical standards of modesty and personal grooming apply to modern practices like the use of makeup?
The modest use of makeup by women is culturally acceptable in the Western world at this time, and does not conflict with the teaching of the Bible.
This subject comes under the general topic of personal grooming. Perhaps the clearest statements in the Bible on a Christian woman's personal grooming are in 1 Peter 3:3-4 and 1 Timothy 2:9-10. Both references counsel women to concentrate upon the "grooming" of their inner character in a way that is pleasing to God, in contrast to placing undue emphasis on their outward appearance.
Personal grooming can and often does reflect one's attitude, as we see amply demonstrated in everyday life. It's easy to spot people—men and women alike—who want to "make a statement" of rebellion through grooming that is against the accepted norm. Grooming that makes a woman stand out as odd or different from culturally accepted norms of good taste detracts from a godly emphasis on her inner character. Such indiscretion—in stark contrast to the above scriptural guidelines—characterized the rebellious "daughters of Zion" mentioned in Isaiah 3:16.