Answer:
The participial phrase is "glowing with colors".
Explanation:
Participial phrases are groups of words that contain a participle and other words. Participial phrases may come at the start of the sentence or be after a noun that it modifies. And if the participial phrase comes at the beginning of the sentence, then it must be followed by a comma before it joins the main sentence.
In the given sentence "the setting sun glowing with colors fascinated us this evening", the participial phrase is "glowing with colors", and modifies the noun "sun". So, there is no need for a comma.
Also, the sentence without the participial phrase can still be a complete sentence. And the participle form of the verb is seen in "glowing".
