Learn Italian: La sedia è marrone.

In Italian, not all adjectives end in -o or -a. Marrone belongs to a group of adjectives that end in -e in the singular. These adjectives use the exact same form for both masculine and feminine words, so it is la sedia marrone (feminine) and il tavolo marrone (masculine).

How would this sentence change if we were talking about multiple chairs?

It would become Le sedie sono marroni. For adjectives that end in -e in the singular like marrone, the plural ending is always -i, regardless of whether the noun they describe is masculine or feminine.

Why does the color marrone come after the noun?

In Italian, descriptive adjectives like colors almost always come right after the noun they describe. You literally say 'the chair brown' (la sedia marrone) instead of 'the brown chair'.

I see an accent mark on è. What happens if I forget to write it?

The accent is very important! è (with the accent) means 'is' (from the verb essere), while e (without the accent) means 'and'. Leaving it out changes the meaning completely.