"They wear white underwear."
Though はく can be written either 履く or 穿く, I think 穿く is technically more correct when it comes to clothing.
履 is more about footgear (履物) and foot protection. So 履く makes sense for shoes. I believe it's even used when talking about putting a tyre on a wheel of a car.
穿く is more about piercing/drilling (穿つ) through a hole (i.e. with one's foot/leg).
The results for したばき (as in 下 + はく) on Jisho.org are quite interesting. ^^
- 下履き / 下履 = "outdoor shoes"
- 下穿き / 下穿 = "undershorts, underpants"
I think it's just that 履 is a jōyō kanji whereas 穿 is only jinmeiyō. So maybe 履 ended up getting overstretched and used like a jōyō alternative of 穿? I wonder if it might instead be more proper to always write はく in kana for those situations and only use kanji when it's for outer footwear?
I think you're exactly right. You can find lots of articles explaining that 穿く is for things like pants/trousers, skirts, and underwear, and 履くis for footwear. But 穿く isn't jouyou kanji, and so google says:
"パンツを穿きます" - 20,700 results
"パンツを履きます" - 78,700 hits
"パンツをはきます" - 31,200 hits
Use hakimasu with things worn from your waist down (belt, skirt, socks, pants, etc.) and use kimasu with things worn on your torso (jumper, shirt, coat, etc.) There's different verbs for things on your hands and for on your head. It seems weird that these are distinguished at first but you'll get used to it owo
Japanese has multiple levels of adjectives. Amongst the colors there are:
"True" い adjectives (Red-赤い-あかい/Blue-青い-あおい/Black-黒い-くろい/White-白い-しろい): These are attached directly to nouns like other adjectives>白いパンツ
Yellow is something of a special case, (黄色い-きいろい) in that it is an adjective, but it requires the 色い/いろい word for color.
The rest of the colors are nouns which include 色/いろ (most of these refer to the color of something: Brown-茶色-ちゃいろ-tea colored/Grey-灰色-はいいろ-Ash colored. Because they are nouns, you need to include の to combine them with)
There are a couple of colors where the native Japanese forms are rarely used, and the katakana version of the English of the color is used(Pink-ピンク色/Orangeオレンジ色). These are also nouns and use の.
TL/DR: Red-赤い-あかい/Blue-青い-あおい/Black-黒い-くろい/White-白い-しろい/Yellow-黄色い-きいろい are the only colors that do not use の when attaching to nouns.
In high school Japanese, I must have missed the memo that パンツ meant "underwear" and not "pants". We were doing a lesson on clothing and the verbs for "to wear" and such, and the teacher said in Japanese that everyone was wearing パンツ. I was wearing a dress that day and proclaimed in front of the class: いいえ、パンツを着ません
下着をつけています。 （主にブラジャー たまにパンツ）
So basically this native speaker says 下着を履いています (haite imasu) for underpants/shorts, 下着を着ています (kite imasu) for long or short sleeved t-shirts, and 下着をつけています (tsukete imasu) for bras and occasionally for underpants.
I think if they are two separate pieces, you might use two separate verbs if you need to specify both, or that つけています might be able to cover both.
I am not Mormon but I guess many LDS members wear a specific type of undergarment as part of their religious practice, to fortify commitment to their faith. The individual above apparently is taking the vague subject of "underwear" in an otherwise entirely unrelated context as an opportunity to deride this for some reason.