On the WMAP image of the cosmic microwave background radiation, are the higher density irregularities the brighter bits or the darker bits?

The averaged CMBR temperature is #\bar{T} = 2.725\quadK#

Given below is a map of temperature fluctuations about this average value, created from the 9 year data of WMAP. In this map the temperature fluctuations about the average value are shown in a scale of #\pm 200 \muK#.

Colour Code:

The pixels in red represent temperatures that are #200\muK# above the average. i.e #T-\bar{T} = +200 \quad\muK#

The pixels in dark blue represent temperature that are #200\muK# below the average. 1.e. #T-\bar{T} = -200 \quad \muK#

What do they mean?: Higher temperature indicates higher matter density.

Density Contrast Field: Fluctuations in mass density are quantified by the density contrast field #(\delta\rho)/\rho#.
#(\delta\rho)/\rho \equiv \frac{\rho-\bar{\rho}}{\bar{\rho}}#, where #\rho# is the density at a point and #\bar{\rho}# is the average matter density.

Temperature Contrast Field: Fluctuations in CMBR temperature are quantified by the temperature contrast field #(\deltaT)/T#
#(\deltaT)/T\equiv\frac{T-\bar{T}}{\bar{T}}#, where #\bar{T}# is the average temperature and #\deltaT# is the fluctuations about this average.

There is direct relation connecting the two which can be deduced from the fundamental principles:

#(\delta\rho)/\rho \propto (\delta T)/T#