What could possibly make an asteroid even the least bit bluish?

[Ann]

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The sort of true color of Pallas?
Source: https://phys.org/news/2009-10-high-reso ... lanet.html

Wikipedia wrote about large asteroid Pallas:

Pallas's visible and near-infrared spectrum is almost flat, being slightly brighter in towards the blue.

How can an object like an asteroid be even the least bit bluish? Here on Earth, extremely few minerals or silicates are bluish. (Or are there some that are?)

I thought objects in the Solar system tended to get progressively darker and redder due to the effects of the ultraviolet light from the Sun. Even interstellar visitor 'Oumuamua is red:

Wikipedia wrote about 'Oumuamua:

Spectra recorded by the 4.2 m (14 ft) William Herschel Telescope on 25 October showed that the object was featureless, and colored red like Kuiper belt objects.

I thought a reddish color was normal for most icy or rocky objects in the solar system. So why would asteroid Pallas be even the least bit bluish?

According to this youtube video, small asteroid 3200 Phaethon is also bluish. Could it be this color?

Ann