  Multiquarks can have two-hadron components and hidden-color components in
their wave functions. The presence of two-hadron components in multiquarks
introduces a potential source of confusion, particularly with respect to their
resemblance to hadronic molecules. On the other hand, hidden-color components
are essential for distinguishing between multiquarks and hadronic molecules. In
this work, we study the hidden-color components in the wave functions of the
tetraquark mixing model, a model that has been proposed as a suitable framework
for describing the properties of two nonets in the $J^P=0^+$ channel: the light
nonet [$a_0 (980)$, $K_0^* (700)$, $f_0 (500)$, $f_0 (980)$] and the heavy
nonet [$a_0 (1450)$, $K_0^* (1430)$, $f_0 (1370)$, $f_0 (1500)$]. Our analysis
reveals a substantial presence of hidden-color components within the tetraquark
wave functions. To elucidate the impact of hidden-color components on physical
quantities, we conduct computations of the hyperfine masses, $\langle
V_{CS}\rangle$, for the two nonets, considering scenarios involving only the
two-meson components and those incorporating the hidden-color components. We
demonstrate that the hidden-color components constitute an important part of
the hyperfine masses, such that the mass difference formula, $\Delta M\approx
\Delta \langle V_{CS}\rangle$, which has been successful for the two nonets,
cannot be achieved without the hidden-color contributions. This can provide
another evidence supporting the tetraquark nature of the two nonets.
