Learn Hardcore Spanish (Latin America): La chaqueta gris está en oferta hoy.

Because chaqueta is a feminine noun, so it takes the feminine article la (plural las). Articles in Spanish must agree with the noun’s gender and number. Note that some regional synonyms for “jacket” have different genders:

Mexico: la chamarra (f.)
Argentina/Uruguay: la campera (f.)
Peru/Bolivia: la casaca (f.)
Many places for a blazer/sport coat: el saco (m.)

Why does the adjective come after the noun in la chaqueta gris?

In Spanish the default order is noun + adjective, especially with colors and most descriptive adjectives. So la chaqueta gris is natural. Putting the adjective before the noun (la gris chaqueta) is unusual and would only appear in poetic or very marked styles.

Should gris change to match the feminine noun, like grisa?

No. Many color adjectives ending in a consonant or in -e don’t change for gender. Gris is the same for masculine and feminine, but it does change for number:

singular: gris (la chaqueta gris / el pantalón gris)
plural: grises (las chaquetas grises / los pantalones grises)

How do I make the sentence plural?

Change everything to plural where needed:

Las chaquetas grises están en oferta hoy. Article: la → las; noun: chaqueta → chaquetas; adjective: gris → grises; verb: está → están.

Why is it está and not es?

Because being “on sale” is a temporary state, and Spanish uses estar for temporary conditions and statuses. Use ser for inherent characteristics:

La chaqueta es barata. (It’s cheap by nature.)
La chaqueta está en oferta. (It’s on sale right now.)

Is en oferta the only way to say “on sale”?

No. Common options (all widely understood in Latin America):

estar en oferta / estar de oferta: on sale (most general).
estar en promoción: on promotion.
estar rebajado/a or estar en rebaja(s): discounted/marked down.
estar en liquidación: on clearance. Be careful: a la venta means “for sale” (available to buy), not necessarily discounted.

Does en oferta mean “available” or “discounted”?

En oferta means discounted or at a special price. If you mean merely “available to purchase,” use a la venta:

La chaqueta gris está en oferta. (Discounted.)
La chaqueta gris está a la venta. (It’s for sale/available.)

Can hoy go somewhere else in the sentence?

Yes. These are all fine, with slightly different emphasis:

Hoy la chaqueta gris está en oferta.
La chaqueta gris está en oferta hoy. (your original)
La chaqueta gris hoy está en oferta. (possible, but less typical) When hoy starts the sentence, many writers add a comma (Hoy, ...), but with a short adverb like hoy it’s optional.

Why does está have an accent? How is it different from esta?

Está (with accent) is the verb form of estar (he/she/it is). The accent marks stress on the last syllable. Esta (no accent) is the demonstrative adjective this (feminine). Example:

Esta chaqueta gris está en oferta hoy. Note: The demonstrative pronoun ésta used to take an accent, but the modern recommendation is to write esta without an accent unless needed to avoid ambiguity.

Any pronunciation tips for the sentence?

chaqueta: ch like English “ch” in “chocolate”; qu before e keeps a hard K sound, and the u is silent: cha-KE-ta (stress on KE).
gris: one syllable; the r is a quick tap.
está: es-TÁ (stress on the last syllable because of the accent).
oferta: o-FER-ta (stress on FER). Spanish vowels are pure: a as in “father,” e as in “met,” i as in “machine,” o as in “told,” u as in “flute.”

Is es en oferta incorrect?

Yes. Use estar with en oferta: está en oferta. The construction ser en is used for the location/time of events (e.g., El concierto es en el parque), not for temporary states of objects.

How would I say “This gray jacket is on sale today”?

Esta chaqueta gris está en oferta hoy. Remember: esta (this, feminine) has no accent; está (is) does.

How would I ask “Is the gray jacket on sale today?” in Spanish?

Two natural options:

¿La chaqueta gris está en oferta hoy?
¿Está en oferta hoy la chaqueta gris?

How do I include the sale price?

You can use a or por for the price:

Está en oferta a 30 dólares.
Está en oferta por 30 dólares. Both are common in Latin America.

Can I drop the article and just say Chaqueta gris está en oferta hoy?

Not in a normal sentence. Spanish typically needs the article with specific, countable nouns: La chaqueta gris... On signs or headlines, you might see the article omitted for brevity: Hoy en oferta: chaqueta gris.

If someone asks me which jacket I want, can I answer just la gris?

Yes. In context, you can use an elliptical answer:

—¿Cuál quieres? —La gris. Here la stands for la chaqueta, and gris is the adjective.

Are there regional words for “jacket” or “gray” I should know in Latin America?

Yes:

Jacket: chamarra (Mexico), campera (Argentina/Uruguay), casaca (Peru/Bolivia), saco (often blazer). Chaqueta is widely understood, but usage varies by country.
Gray: gris everywhere; in some places you’ll also hear plomo for the color gray (e.g., parts of Peru/Ecuador).

Can I say La chaqueta gris está rebajada hoy?

Yes. Estar rebajado/a means “to be marked down/discounted.” You could also say La chaqueta gris está en rebaja or La chaqueta gris tiene un descuento (it has a discount), though está en oferta and está rebajada are the most idiomatic for clothing.