A lot of color words have the ㅎ ending. For example, 빨갛다 (red) falls in this category. There are other words that are not color words that have a ㅎ ending. 그렇다 (to be in that way, to be like that) is another example

In the standard polite present tense form 그렇다 will be 그래요. Drop the 다 and the ㅎ and change the 어 vowel in 러 to 애, which will become 래. The past tense of 그렇다 will be 그랬어요.

In the deferential polite present tense form 그렇다 will be 그렇습니다. Drop the 다 in 그렇다 and add 습니다. In the past tense it’ll be 그랬습니다.

In the honorific polite 그렇다 will be 그러세요. Drop the 다 and ㅎ and add 세요. The past tense will be 그러쎴어요.

The honorific deferential of 그렇다 will be 그러십니다. Drop the 다 and ㅎ and add 십니다. The past tense will be 그러셨습니다.

Other words that will have conjugation changes like 그렇다 are :

이렇다 (to be in this way, to be like this)

저렇다 (like that, that way)

노랗다 (yellow)

하얗다 (white)

However, just because a word ends in ㅎ doesn’t mean that it will be conjugated like 그렇다. Words like 많다 (to be many, to be a lot), 싫다 (to dislike), 좋다 (to like) will not conjugate like 그렇다. They will conjugate in the normal manner. For example 많다 in the standard polite present tense form will be 많아요.