The answer is ROSY, four letters. Rosy began as a plain color word meaning pink, the shade of a rose, and then grew a second life describing outlooks, forecasts and pictures of the future. Puzzles almost always want that second sense.
Where the literal and figurative senses part company
The literal sense stayed attached to bodies and to light. Rosy cheeks, a rosy glow, a rosy dawn. Homer’s standing epithet for daybreak, usually rendered in English as rosy fingered, is the oldest version of that image most readers ever meet, and every use of it is about an actual color in the sky.
The figurative sense attached itself to something completely different, namely predictions. A rosy forecast, a rosy picture, a rosy outlook. Look at what those three nouns share: each is an account of something that has not happened yet. A person can have a rosy complexion and a rosy projection in the same sentence, and the word is doing unrelated work in each half, with no signal marking the switch.

Rose tinted glasses and what the idiom is claiming
The phrase rose colored glasses, or rose tinted spectacles in British use, is where the figurative sense set into a fixed expression. The origin is not firmly documented, and accounts that hand you a confident date are usually guessing, so it is worth treating those with suspicion.
What the phrase asserts is clear enough, and it is sharper than it looks. It does not accuse the optimist of lying or of failing to look. It accuses them of seeing accurately through a filter that flatters everything equally, which means the error is systematic rather than occasional. That is why the idiom carries a faint sting that the plain word optimistic does not.
The vocabulary of too much optimism
English keeps a separate set of terms for optimism carried past the point of usefulness: Pollyanna, starry eyed, wide eyed, naive, and the rose tinted family itself. Constructors reach into that group whenever the clue carries a hint of judgement.
The tell is almost always a qualifier. Blindly optimistic, unrealistically hopeful and relentlessly cheerful all steer away from the neutral synonyms, and none of the words in the second group will fit four squares. An adverb in the clue is worth reading before you start counting the grid.

Matching the register to the slot
Synonym clues like this are graded by vocabulary rather than by trickery, so the length is effectively telling you which register the editor is working in.
| Letters | Answer | What it describes |
|---|---|---|
| 4 | ROSY | An outlook or a forecast |
| 5 | SUNNY | A disposition |
| 6 | UPBEAT | A person or a mood |
| 7 | HOPEFUL | Neutral and general |
| 7 | BULLISH | Markets, forecasts, investors |
| 8 | SANGUINE | Literary, later in the week |
| 9 | POLLYANNA | Optimism treated as a fault |
Early week puzzles stay with ROSY and SUNNY. The same definition later in the week arrives wanting SANGUINE, or a two word phrase. Knowing which day’s puzzle is in front of you narrows seven candidates to two before a single crossing letter is in place, which is a larger saving than most solvers give it credit for.