Final answer:
Yes, it is okay to have notes outside of a given key in music, which are called 'accidentals' and are used for various expressive reasons, such as adding tension or color to a piece.
Step-by-step explanation:
This question is related to the realm of music theory within the Arts. In music, keys are a set of pitches or scale tones that form the basis for musical composition. Within a particular key, some notes are considered 'diatonic', meaning they belong to the scale of the key in which the piece is composed. However, it is indeed okay to have notes outside of a given key. These are called 'accidentals', and they are used for various expressive reasons, such as to add tension, to modulate to a different key, or to include chromatic or non-diatonic tones that add color and interest. For example, in the key of C major, notes such as F# or Db are not part of the C major scale. Yet, composers might use these notes for expressive effect or as part of a chord progression leading to a modulation.