See attached project.
Yes, the TChartStyles are mean for repetitive action. So, you must prevent it to become repetitive, you must cover the entire axis space by stripes, they only repeat themselves if any axis extent it left.
Add a TListChartSource, it will define the points where the color changes. In your example, it is only one, 150. Add code to write this number into the listchartsource, only this more, no more!
Then add a second x axis (ObjectTree, right-click "AxisList" --> "Add item"). Select the new axis, it is a y axis by default, but by setting "Alignment" to alBottom it becomes an x axis. Select both x axes, set their "Group" to any non-zero number (e.g. 1), this causes both x axes to be drawn on the same line. Select Marks of the new x axis, hide the labels by setting "Visible" = false. Set "Source" to the ListChartSource added above. Set "Stripes" to the TChartStyles. You need two stripes, the first one blue, the second one yellow. The first stripe reaches from "neg inifinity" up to the point defined in the list chource, the second one from this point up to "pos infinity".