I have a question after reading an article online. It seems to indicate the proper dress code must be white because Christians wearing white clothing is a sign of purity. So it is sinful for men to wear black clothing on services on Sunday? Is a black shirt or trousers immodest and wrong?
I suspect you misunderstood the intentions of the article you found. In the symbolism of the Bible, white represents purity or righteousness. Thus, if an author wishes to emphasize that someone is righteous, they are described as wearing white. For example, "Then one of the elders answered, saying to me, "These who are clothed in the white robes, who are they, and where have they come from?" I said to him, "My lord, you know." And he said to me, "These are the ones who come out of the great tribulation, and they have washed their robes and made them white in the blood of the Lamb"" (Revelation 7:13-14). We know this is figurative language because you can't wash anything in blood and expect it to physically come out white. But as a symbol, we know that Jesus' blood was shed to cleanse us from sin and, thus, makes us pure again.
Figurative language is not meant to be applied physically. It is a visual word picture to relay information. The rules for your physical dress is to be modest in our clothing choices. There are no laws about what colors we choose to wear.