Unless we were talking about a specific set of colours e.g. "The man loved the fabrics. He talks about the colours."

You may try to put the sentence in singular:

• je mange des pommes -> une mange une pomme = I eat an/one apple / direct and indefinite object
• je parle des pommes -> je parle de la pomme = I talk about the apple / indirect and specific object

It can be "he talks about colours" as the plural of "he talks about a colour" (or "one colour"), to mean "an undefined number of colours".

And that would also mean "colours" in general.

talk about something = parler de quelque chose

in French "quelque chose" has to get its usual article, in this instance "les couleurs".

but when "de" is followed by "les", there is a contraction: de+les = des

so "des couleurs" is not the plural of "une couleur", but the plural of "de la couleur" -> des couleurs.

therefore, in English you need to translate to "about the colors"

Indeed, the verb makes a lot of difference, whether it is transitive (direct object) or not (with a preposition).

Manger, prendre, couper, boire... are directly transitive:

• il mange une baguette, elle achète des baguettes (des = plural of un/une)

but with uncountable "mass words", French add a preposition to mean "some":

• nous coupons du pain (uncountable), vous buvez de l'eau (uncountable) et de la bière (uncountable)

Parler de, penser à... are used with prepositions, which need to adapt the construction of the object.

• je parle d'une baguette (about one), il parle de baguettes (about more than one),nous parlons de la baguette (about the), vous parlez des baguettes (about the = de+ les = des))

In addition, appreciation verbs (aimer, détester, haïr, préférer, apprécier) naturally introduce definite articles

• j'aime les légumes, mais je préfère les fruits, il déteste l'injustice, elle préfère la biologie...

No it wouldn't, Jacob and a good morning to you, (well, it is 0720 in the morning here in England, anyroad.) This just says that he is speaking of colours, not that colours are being emitted from his mouth. (Des Coleurs Sortent De Sa Bouche.)

"des" is not the indefinite article (plural of "une couleur": in singular: "il parle d'une couleur".

it is preposition "de" + definite article "les", contracted.

verb "parler de" uses preposition "de", while "talk about" uses preposition "about"

There is none.

Des, the article, means some.
Des, the contraction means of the, from the, or some.
https://en.wiktionary.org/wiki/des#French

Note: In this sentence, the phrase of the is another way of saying about the.

"Les" is indeed "The" before a plural noun. "Des" as an article="Some" but "Des" is also a contraction of "De+Les" = "Of The" and as SongbirdSandra says above; in this task "Of The" is another way of saying "About The".

1) "des" is either an indefinite article, plural of "un/une"

2) or a contracted definite article where preposition "de" is merged with definite article "les": de+les = des

now, in terms of meaning and translation to and from English, there are several cases:

1) "un chien = a/one dog" is singular; "des chiens = (some) dogs" is plural.

• In English, you don't need an article to mean "an undefined number of dogs or more than one dog".
• But in French, "des" is required.

2) "les noms des chiens" = literally: "the names of the dogs", where you understand that the names belong to the dogs.

• In English, you will not use "of the" but the possessive case: "the dogs' names"
• But in French, there is no such construction, so you have to keep: "les noms (de+les=) des chiens"