Fix a prime \(p\) the chromatic tower of a Thom spectrum \(X\) is the tower of Bousfield localization:
\begin{align*}
X \rightarrow \cdots \rightarrow X _ { E ( n ) } \rightarrow X _ { E ( n - 1 ) } \rightarrow \cdots \rightarrow X _ { E ( 0 ) }
\end{align*}
where \(E(n)\) is the \(n\)th Johnson-Wilson spectrum \((E(0) = { \mathsf{H} }{\mathbf{Q}}\), by convention) with
\begin{align*}
E ( n ) _ { * } = \mathbb { Z } _ { ( p ) } \left[ v _ { 1 } , \dots , v _ { n - 1 } , v _ { n } ^ { \pm } \right]
\end{align*}
The fibers of the chromatic tower
\begin{align*}
M _ { n } X \rightarrow X _ { E ( n ) } \rightarrow X _ { E ( n - 1 ) }
\end{align*}
are called the monochromatic layers.