left join and where - Mailing list pgsql-sql

hello,
I'm a beginner and I have a trouble with SQL and Access 97
I try to explain the problem:

I have a table colori:

ID  colore
1   red
2   blu
3   green

and a table Vendite

ID colore anno quantita
1   red    1     10
2   blu    1     20
3   green  2     30

I want a query that return all "quantita" but only for a year (for example
if year =1, I don't extarct green)
The result must be:

colore anno quantita
red     1     10
blu     1     20          
green       
------------------------------------

I use this SQL code

SELECT colori.colore, vendite.anno, sum(vendite.quantita)
FROM colori
LEFT JOIN vendite ON colori.colore=vendite.colore
WHERE vendite.anno=1 OR vendite.anno Is Null
GROUP BY colori.colore, vendite.anno

But the result is

colore anno quantita
red     1     10
blu     1     20          

How can I get the correct result

Thank's for the help

Andrea