According to our current understanding of particle physics, neutral quarks do not exist as isolated particles. Quarks are elementary particles that carry fractional electric charges and interact through the strong force, mediated by particles called gluons. In the framework of the Standard Model, which describes the known elementary particles and their interactions, quarks come in three "colors" (red, green, and blue) and combine to form colorless particles called hadrons, such as protons and neutrons.
The strong force obeys a property known as color confinement, which means that quarks cannot exist in isolation but are always found in bound states. This is why we observe quarks only in combinations that result in colorless hadrons. This confinement is due to the fact that the strong force becomes stronger as quarks are separated, making it energetically unfavorable to have isolated quarks.
Regarding anomalies in the strong force interactions, anomalies typically arise when experimental measurements do not match the predictions of a theory. However, in the case of the strong force interactions, anomalies related to the existence of neutral quarks are not observed or predicted within the Standard Model.
Neutrinos, on the other hand, are neutral leptons and do not carry color charges. They interact solely through the weak nuclear force, which is responsible for processes such as beta decay. Neutrinos were initially postulated to explain observed anomalies in weak interactions, such as energy-momentum conservation in beta decay. Subsequently, experimental evidence confirmed the existence of neutrinos, and they were incorporated into the Standard Model as essential components of the particle spectrum.
It's important to note that there are speculative theories beyond the Standard Model, such as theories involving "leptoquarks" or other exotic particles, which could potentially introduce neutral quarks or other types of colored particles with different properties. However, these theories are still under active research, and no conclusive experimental evidence for the existence of such particles has been found thus far.