Water-absorbent resin particles

Water-absorbent resin particles having a gel brightness L* of 8 to 44 measured by a method including the following steps (A), (B), and (C) in this order,

• (A) uniformly scattering 0.1 g of water-absorbent resin particles in a colorless and transparent round cell for a color-difference meter, the round cell having an inner diameter of 30 mm,
• (B) adding 5.0 g of ion-exchanged water to the round cell to cause the water-absorbent resin particles to absorb water, and
• (C) measuring a brightness L* of an obtained gel on a black background after five minutes from the addition of the ion-exchanged water, wherein
• the water-absorbent resin particles comprise crosslinked polymer particles having a structural unit derived from an ethylenically unsaturated monomer that is at least one selected from the group consisting of (meth) acrylic acid and salts thereof, 2-(meth) acrylamide-2-methylpropanesulfonic acid and salts thereof, (meth) acrylamide, N, N-dimethyl (meth) acrylamide, 2-hydroxyethyl (meth) acrylate, N,N-diethylaminoethyl (meth) acrylate, N,N-diethylaminopropyl (meth) acrylate, and diethylaminopropyl (meth) acrylamide,
• an amino group in the ethylenically unsaturated monomer may be quaternized,
• a degree of neutralization of the ethylenically unsaturated monomer by an alkaline neutralizing agent is 10 to 100 mol %,
• an amount of the ethylenically unsaturated monomer is 70 to 100 mol % with respect to a total amount of monomer for the water-absorbent resin particles, and
• a carboxyl group or an amino group of the ethylenically unsaturated monomer participates in surface crosslinking of the water-absorbent resin particles.