Can someone EXplain the Spartan undersuits

OK so when we first see majestic there in some like tight outfit with pants on then when they are getting there armor put on they are in some kinda black and blue muscle suit thing and whenever i look it up there seems to be no depiction that these are two different suits one has a plain black image while the other looks almost like a spider man suit design on the actual material im just kinda confused i know i aint seeing things these are totally separate suit correct. why do some people say they are the same thing. Just would like some clarification on this.

The first time we see the undersuits, I don’t know. Second time, when majestic gets suited up, I would assume that those undersuits are standard for spartans, as you can’t cover every body part with armor.
But yes, it is odd.

Taken from Halo Wikia

The armor’s outer shell is composed of a multilayer alloy of remarkable strength and has been augmented with a refractive coating capable of dispersing a limited amount of Covenant energy weapon strikes. The suit contains a gel-filled layer underneath a thick black armored bodysuit. The gel layer regulates temperature and can re-actively change its density. The inner skinsuit is made of a moisture-absorbing synthetic material linked to an environment control computer and the occupant’s UNSC-issue neural interface.

-SNIP-

Titanium Nanocomposite Bodysuit: Sandwiched between the external armor and the internal padding is a thick black armored bodysuit. This suit has numerous functions, small but vital to the safety and survival of the wearer. The bodysuit is made of a titanium-based material, making it very strong and yet very flexible. It also serves as another layer of protection against ballistics attacks and is coated with a heat resistant material to disperse heat from Plasma weapons.

There are more layers and this link has a lot more information about suit versions and layers, I recommend giving it a read.