Color coding

Hello,
Sorry for this ultra noob question, but why some functions are coloree in orange when entered and some are not. Some are in bold some are not.
Example :
Char is in orange but dtostrf is in regular black font?
Serial, setup are in bold?
Why is that?
Very sorry for this, but this is all new to me.
Thank you.

There is a file full of "keywords" and when the IDE sees any of the words in that file it colors them orange (or blue in some cases). That's all it means. That the people who wrote the IDE (or some library in the case of library keywords.txt files) decided to color those words orange. In terms of what they mean to the program, they don't mean squat. You can put any word you want in a keywords.txt file in a library in the IDE folder and it will start turning orange.

Keywords.txt

There are other IDEs where functions all turn one color and defined constants turn another color and colors all mean something. Those IDEs actually parse through the code and identify those things and color them appropriately and you can use the color changes to know that you've written a word that was already defined somewhere else. What the Arduino IDE does is a very poor attempt at replicating that.

Thank you for the clairifcation.
Yes I did I saw that in each librairie folder (*.h + *.cpp) I can see a keyword.txt.
What about functions like int, char, string ect... I can't find the keyword.txt for these.
I'm not trying to reverse engineer everything, but just trying to understand how this is all built in.

There’s another keywords.txt file in the lib folder wherever you installed the IDE that has the stuff for the IDE itself.

Delta_G, exactly what I was looking for.

For those looking for this, that keyword.txt is located at :

C:...yourpath to...\arduino-1.0.6\lib\keywords.txt

In there we fine the explanation as to why some of the "default" wordings/calls appears in orange.