Tinta vs. tinto
The Portuguese words tinta and tinto look and sound similar but have distinct meanings and grammatical functions. In short, tinta is a noun referring to a substance like paint or ink, while tinto is usually an adjective meaning red (for wine) or dyed.
Tinta
A2Tinta is a feminine noun that refers to the physical substance used for coloring. It translates to paint, ink, or dye.
Preciso de mais tinta azul para terminar o quadro.
(I need more blue paint to finish the painting.)
A minha caneta favorita ficou sem tinta.
(My favorite pen ran out of ink.)
Compramos uma lata de tinta para a parede da sala.
(We bought a can of paint for the living room wall.)
Ela usou uma tinta de cabelo para ficar loira.
(She used a hair dye to become blonde.)
Cuidado para não sujar a camisa com tinta da impressora.
(Be careful not to stain your shirt with printer ink.)
Tinto
A2Tinto is primarily an adjective meaning dyed, tinted, or, most commonly, red when referring to wine (vinho tinto). As an adjective, it must agree with the noun's gender and number (tinto for masculine, tinta for feminine). It can also be used as a noun (o tinto) as a shorthand for red wine.
Este restaurante serve um excelente vinho tinto.
(This restaurant serves an excellent red wine.)
O artesão usou um tecido tinto com plantas.
(The artisan used a fabric dyed with plants.)
Para o jantar, vou querer um copo de tinto, por favor.
(For dinner, I would like a glass of red wine, please.)
A camisa foi tinta de preto.
(The shirt was dyed black.)
Seus olhos estavam tintos de raiva.
(His eyes were tinged with anger.)
Summary
The main difference is grammatical and semantic. Tinta is a noun: it's the name of a substance (paint, ink). Tinto is an adjective: it's a quality describing something that has been colored or, most famously, describes red wine. While tinta can be the feminine form of the adjective tinto (e.g., camisa tinta - dyed shirt), context always clarifies whether it means the substance paint or the quality dyed.