Hello everybody!

I wanted to ask about the difference between using "esti" with adjectives and using the verb-form of an adjective to say how something is. For example, what is the difference between saying "Ĝi estas blua" and "Ĝi bluas (conjugated form of blui)"?
Is there a difference? When do you use what, or does it not matter?
Thanks in advance!

There are some adjectives where the verb form has a different meaning; I can't think of examples off the top of my head, but I know there are some. Aside from that, it seems, from my experience, that it's more common to use the verb form when talking about transient conditions (mi ĝojas, li malsatas, vi pravas) than for attributes or characteristics (li estas alta, ĝi estas ligna, ŝi estas bela). But those are just stylistic generalizations, not hard-and-fast rules.

Tthank you very much!

In the classic view of word formation in Esperanto, the various components were viewed as though they were themselves 'words' and the meaning of any compound was whatever the joining of these words seemed to be reasonably applicable to in the real world.

So for the meaning of blui you have to consider what there is to be described that this verb might apply to.

Of course you could search a million words of text and never find 'blu (sic) used as a word nor 'i', though you would find plenty of examples of 'blua' and 'bluo', and plenty of examples of infinitives ended in 'i'.

Later a whole theory arose depending on ascribing meanings to roots by placing them in grammatical classes, so 'blu' was then considered to be 'really' 'blua', and a superstructure of complex rules of derivation were produced - which some might think shows that grammarians have too much time on their hands.

It also produced in some cases uncertainy about which class a root belonged to - I have a 1925 much reprinted dictionary which lists 'bluo' as the head word.

Anyway, whether blui is seen as blu-i or blua-i, there still remains from a practical point of view whether there is some thing in the real world to which the verb 'to blue' might apply. However because of how verbs are used, you can say that the meaning is either a state or an action.

My guess would be if you asked an Esperantist what the verb blui means, the reply would be that it means to be blue, but with a suggestion some action or process of being blue is involved. Perhaps, something like to shine blue.

But it doesn't mean to turn blue - that's 'bluiĝi', nor to make blue - that's 'bluigi'.

(Note whilst in English we have whiten, to make white (ie blankigi) we don't have a corresponding verb for to make blue, and 'I blued the lot on wine women and song is nothing to do with colour)

Judging by searches in the Tekstaro the use of colour words as verbs seems to be fairly uncommon and some hardly used at all in this way. 3 hits for bluas, 1 for flavis, none for brun used verbally.

However, reasonable returns for blanki and nigri.

Wow! Thanks for such an in-depth explanation, I did not expect that!
I much appreciate it!

I am not and do not claim to be an expert, but Christa627's explanation makes a lot of sense to me: a transient condition (-as) versus a natural attribute or characteristic (esti -a).

I too would second Christa's explanation. You could use "blui" for "radiate blueness" or something similar according to the context.

Ruĝi vs esti ruĝa: verb form implies that being red is an inherent aspect of the verb.
Tial, I would consider "mia aŭtomobilo ruĝas" quite strange. The redness of the car is not something that is intrinsically part of the verb (think of ruĝi = *ruĝesti but NOT equivalent to "esti ruĝa").
However, the sky can be of many colours in the evening. In fact, saying that "la ĉielo estas ruĝa" seems to imply that it is generally red, pointing out a permanent quality (the connotation could potentially be linked to the ser/estar difference in Spanish, or even long/short forms in Russian adjectives, but it is more subtle in Esperanto). "La ĉielo ruĝas" would point out that the sky "is being red", which is more significant than "the sky is red".

Ambiguous cases:
Suppose you are heating up a metal until it is red hot. Is it "ruĝas" now? It depends on how you think about it. Saying "ruĝas" can imply that it does not have that colour when cold. However, "esti ruĝa" should be acceptable if you are comparing it with a white stone that is next to it. When the sentence is exclusively about it being red -as a state-, ruĝas is preferable. When the sentence is either comparing it to other thing based on it or describes a general trend (la ŝtalo estas ruĝa nur kiam la temperaturo estas supra ##ºC). Note that "ruĝas" can be used there but instead of describing its general state above that temperature, it says that it "is being red" above that temperature.

La ĉielo estas blua. Yes, the sky is blue. La ĉielo bluas. Perfectly acceptable, but implies that it isn't always like that: think about the difference between cloudy and sunny days. Subtle differences that have different connotations but are otherwise acceptable.

There are some adjectives where the verb form has a different meaning; I can't think of examples off the top of my head, but I know there are some

Still wondering about a good example of this, Christa, but another thread threw up a good example of meaning change with change of part of speech, but in that case noun to adjective - rozo (flower), roza (colour pink).