Questions & Answers about Vi måste välja rätt färg idag.
Since this lesson is about 'which', how would I ask 'Which color must we choose today?'
Because färg is an en-word, you would use vilken. The question would be: Vilken färg måste vi välja idag? Notice how the verb måste comes right after the question phrase Vilken färg, keeping the verb in the all-important second position!
Why is the verb välja in its infinitive form instead of the present tense väljer?
Just like in English, the modal verb måste (must) is followed directly by the infinitive form of the next verb. So we use välja (to choose) without adding the usual present-tense r at the end.
Is rätt an adjective here, and does it change depending on the noun?
Yes, rätt means right or correct. Normally adjectives change depending on if the noun is an en-word or an ett-word. However, rätt is a convenient exception: it looks exactly the same whether you say rätt färg (en-word) or rätt svar (right answer, ett-word).
Can I put idag at the beginning of the sentence to emphasize 'today'?