We know that Jonas looks about the same as most other children his age in his community. Because of the principles of Sameness, everyone in the community looks as similar as possible.

Unlike the majority of his community, Jonas develops the ability to see colors. The first color he sees is red, though he doesn't realize what the quality of color is at first. One of the first places Jonas sees the color red is in the skin color of people in an audience, so he shares this same tone.

We can also infer that Jonas is in pretty good physical shape. Food in their community is strictly controlled; Jonas once was the cause of a public reminder that "SNACKS ARE TO BE EATEN, NOT HOARDED" after accidentally taking an apple from the recreation center. There is a food delivery crew and a food collection crew; it seems that families are able to keep very little, if any, food inside their homes for private consumption. Additionally, Jonas's younger sister, Lily, is envious of the "gentle exercise periods" afforded to Birthmothers. It seems that rigorous exercise is another requirement of citizens, so Jonas is likely trim and athletic.

The principles applied to achieve Sameness have not fully mastered making everyone look completely the same, and Jonas's pale eyes are unusual in their community. Both the Giver and Gabriel share these "pale," likely blue, eyes.

Like other citizens, Jonas wears a tunic. His hair is neatly trimmed, as is expected of boys his age. Jonas physically blends into his world, which is the expectation in his community.

When Jonas is discussing his future ceremony of Twelve with his mother and father, the narrator tells us that his father reached over and "stroked [his] neatly-trimmed hair."  This is really all the information we get about his particular style of hair, or rather, his indistinctive style since we learn that the age groups share a haircut.

It's true that Jonas's eyes make him stand out from others in the community—so much so that his sister, Lily, points out (rather rudely in Jonas's view) the fact that the newchild, Gabriel's, eyes are just like Jonas's.  

"Oh, look!" Lily squealed in delight. "Isn’t he cute? [....] And he has funny eyes like yours, Jonas!" Jonas glared at her. He didn’t like it that she had mentioned his eyes.

The most important thing about Jonas’s appearance is his eyes.  Jonas’s eyes separate him from the rest of the community, and seem to genetically predispose him to the “gift” of Capacity to See Beyond.

Jonas has pale eyes, when everyone else’s are dark.  There are few people with pale eyes: Gabriel, The Giver, and a female Five.

No one mentioned such things; it was not a rule, but was considered rude to call attention to things that were unsettling or different about individuals. (ch 3, p. 20)

Jonas looks like everyone else in most other senses.  He has brown hair, and it is cut short (everyone has the same haircut, based on age).

Jonas is white.  We know that there used to be different skin tones, but they eliminated them when they chose Sameness.

Today flesh is all the same, and what you saw was the red tones. Probably when you saw the faces take on color it wasn't as deep or vibrant as the apple… (ch 13, pp. 94-95)

Jonas wears a tunic, which is kind of like a long shirt, and pants.  He dresses like everyone else.

Jonas's eyes are significant because they separate him from the others.  Even though it's not polite to talk about his eyes, it is clear that Jonas has always been a little different.

Lowry, Lois (1993-04-26). The Giver (Newbery Medal Book). Houghton Mifflin Harcourt. Kindle Edition.