Different colors implies different materials and R values. It could be some homes are getting an upgraded attic insulation. It could also mean the the builder has hired more than one insulation sub-contractor who use different materials but are installing the same R value.

Pink and yellow are usually fiberglass. White and grey/brown are usually cellulose. Unusual that they would use different materials in in the same housing tract but as long as the R value is the same its probably no big deal.

how can i be sure they are using R38 in the ceiling attic as specified in the contract?

Find out what material will be used. This will give you the R value per inch. Then find out how many inches are being applied and calculate the R value. If possible inspect the attic yourself to verify the insulation has applied uniformly.

I believe Owens Corning has a trademark on the color pink for structural fiberglass insulation. I believe all of It's products, and only its products, are pink. Products from other manufacturers will be other colors.

If the are using batts then the R value is in the wrapper. They may be doing two layers one faced followed by an unfaced top layer in a perpendicular direction. There are 12 Inch batt insulation which is rated for R38 so it is not necessary to use two layers. The batt should be faced if only one layer is used.

I get the feeling the work is being done at low cost and corners are being cut. Ask a lot of questions and take photos.

If the builder buys his insulation from different vendors, he is liable to get a better price due to competition rather than a single source.

Yes, of course. In the case of the insulation contractor, I believe that because of their size, they able to deal directly with the manufacturers and not distributors.

I'm sure a development builder (which this is intimated to be, with the reference to "different homes) gets competing bids for as much as possible, perhaps ranging from lumber to roofing materials and pipe materials and whatever else they can buy and source in bulk, to get better prices on materials.

It doesn't matter. Builders here do not buy insulation. Insulation sub furnish it. The issue is with volume pricing. Most Insulation subs have very significant discounts. If you buy insulation at lowes and install it yourself - you pay nearly same money as having it provided and installed.

I believe there is such a thing today as recycled fiberglass. It is all sorts of colors, mostly grey like this.

is white better?

Is the roof deck being insulated in the other house? Is this what is planned for your house?

The workmanship seems poor and I don't see any moisture barriers. I would be more concerned how the insulation is being installed then the color.

the white and brown insulation is from different houses. I dont know why they use different one. and the brown one looks like a much more cleaner job