Is there a difference between "this is a..." and "it is a..." ? Both seem to be "Ez egy..."
There isn't. Hungarian doesn't have a specific word for "It", so in some contexts "Ez" or "Az" will be used, in others, it simply isn't said.
can we drop the egy in this sentence? Is Ez piros alma the same as Ez egy piros alma?
Yes, you can do. The hungarian indefinite article is much less used compared with the english or the german one :-)
"Ez egy piros alma" focusses on the fact, that there is ONE apple (and not two for instance).
Actually, in this sentence you cannot drop "egy". "Ez piros alma" as a sentence on its own is grammatically incorrect, unless you really want to emphasize that this is a red apple and not a (for example) yellow one. Even then I think the sentence sounds kind of unnatural.
Could this sentence mean "Is this a red apple?" if a question mark was put at the end e.g. Ez egy piros alma?
Yes, that is possible. Only the speaking melody of the sentence is different.
It depends on that, what you want to say :-)
egy alma = an apple / az alma = the apple
egy piros alma = a red apple / a piros alma = the red apple
If the adjective is following the noun, it means something else.
Egy alma piros. = One apple is red.
Az alma piros = The apple is red.
If you put the adjective on the first place of the sentence, you put the focus on that word.
Piros az alma. = The apple is RED (... and not green).
I hope, it is clear for you
In the third person the verb "to be" (i.e. "van") is omitted. Therefore when you would say "ez van egy piros alma" that is grammatically incorrect, so you have to say "ez egy piros alma".
What the difference between "vörös" (and sometimes "veres") and "piros". Is vörös more like blood and piros mor like fire?
I heard about the fact, that vörös would be an equvalent for the color of red vine ("bordeaux"), but I think, that's not correct at all.
A lot of red things, which might have an emotional context, are used rather with vörös than with piros. So red wine is vörös bor, Mars as the red planet is vörös bolygó, the red flag of the communism is vörös zászló as the red place in Moscow is vörös tér in Hungarian, Manfred von Richthofen called "the red baron" is in Hungarian "vörös baró" and finally red hair on the head is vörös haj.
I thought that natural colours, like blood, wine... are vörös, and artificial colours like race cars or traffic signs are piros. But apparently that's not correct, as I'd expect apple to be vörös then.
That is partially true though, we do say that the traffic light is "piros" while blood and wine are "vörös". Usually "vörös" refers to deep red and "piros" refers to light red, but note that there is no strict rule for this. There are some examples however, where using red is obligatory, like those listed above by Andreas305.
you can usually use both in any context.there are some exceptions,like "vérvörös" means bloodred.we don't say "vérpiros"."veres" is kind of an older form of "vörös",but still used.
Could this sentence be translated (mot-a-mot) to 'this a red apple'? I don't think i understand the meaning and use of egy, and many times there doesn't seem to be a verb in the sentence.
well, yes, mot-a-mot it translates as This a red apple. In english it lacks a verb, because you cannot remove the verb "is" in english as you can in hungarian. So, in english it is This is a red apple.
In hungarian, verb van (is) is often ommited and sentence is considered fine without it. However, you must put it back in english. So sentence like O lany. Is really O lany van and means She is a girl. If you cannot see the verb it is third person singular van. Egy means a (indefinite pronoun) and a /az means the (definite pronoun). Unfortunately, egy can also often be ommited. So you can have Ez (egy) piros alma (van). Words in brackets are for emphasis (this is A red apple, ONE apple and this IS a red apple).