Fix Cognitive Load fillcolor crash, pre-select Visual ROIs in Brain Viewer

- Fix hex-to-rgba conversion for confidence band fill colors (was producing
invalid color strings like 'rgba(00D2FF' instead of 'rgba(0,210,255,0.15)')
- Pre-select Visual region group in Brain Viewer so ROI highlighting is
visible on first load

pages/2_Cognitive_Load.py

@@ -92,9 +92,16 @@ for dim, color in dim_colors.items():
         ci_hi = np.percentile(boot_arr, 97.5, axis=0)
         t_axis = timeline_df["time"].values
 
+        # Convert hex color to rgba for fill
+        if color.startswith("#"):
+            r, g, b = int(color[1:3], 16), int(color[3:5], 16), int(color[5:7], 16)
+            fill_color = f"rgba({r},{g},{b},0.15)"
+        else:
+            fill_color = color
+
         fig.add_trace(go.Scatter(x=t_axis, y=ci_hi, mode="lines", line=dict(width=0), showlegend=False))
         fig.add_trace(go.Scatter(x=t_axis, y=ci_lo, mode="lines", line=dict(width=0),
-                                 fill="tonexty", fillcolor=color.replace(")", ",0.15)").replace("rgb", "rgba").replace("#", "rgba(") if color.startswith("#") else color,
+                                 fill="tonexty", fillcolor=fill_color,
                                  showlegend=False))
 
     fig.add_trace(go.Scatter(x=timeline_df["time"], y=y, name=dim, line=dict(color=color, width=2)))

pages/5_Brain_Viewer.py

@@ -51,11 +51,11 @@ with st.sidebar:
                             format_func=lambda x: {"#0E1117": "Dark", "#000000": "Black", "#1A1A2E": "Navy"}[x])
 
     st.subheader("ROI Highlighting")
-    roi_groups_selected = st.multiselect("Region groups", list(ROI_GROUPS.keys()))
+    roi_groups_selected = st.multiselect("Region groups", list(ROI_GROUPS.keys()), default=["Visual"])
     available_rois = []
     for g in roi_groups_selected:
         available_rois.extend(ROI_GROUPS[g])
-    selected_rois = st.multiselect("Specific ROIs", available_rois, default=available_rois[:5] if available_rois else [])
+    selected_rois = st.multiselect("Specific ROIs", available_rois, default=available_rois[:4] if available_rois else [])
     show_labels = st.checkbox("Show ROI labels", value=True)
 
 # --- Load Mesh ---