use standard text colors for constants buttons

This fixes constants button text being unreadable in dark mode.

colors.ui

@@ -281,6 +281,33 @@
           </property>
          </widget>
         </item>
+        <item row="7" column="0">
+         <widget class="QLabel" name="textLabel13">
+          <property name="text">
+           <string>&amp;Constants:</string>
+          </property>
+          <property name="wordWrap">
+           <bool>false</bool>
+          </property>
+          <property name="buddy">
+           <cstring>kcfg_ConstantsButtonsColor</cstring>
+          </property>
+         </widget>
+        </item>
+        <item row="7" column="1">
+         <widget class="KColorButton" name="kcfg_ConstantsButtonsColor">
+          <property name="text">
+           <string/>
+          </property>
+         </widget>
+        </item>
+        <item row="7" column="2">
+         <widget class="KColorButton" name="kcfg_ConstantsFontsColor">
+          <property name="text">
+           <string/>
+          </property>
+         </widget>
+        </item>
        </layout>
       </item>
       <item>

kcalc.cpp

@@ -2169,6 +2169,11 @@ void KCalculator::setColors() {
 		qobject_cast<KCalcButton*>(btn)->setTextColor(opFontColor);
 	}
 
+	const QColor coFontColor(KCalcSettings::constantsFontsColor());
+	foreach(QAbstractButton *btn, const_buttons_) {
+		qobject_cast<KCalcButton*>(btn)->setTextColor(coFontColor);
+	}
+
 	KColorScheme schemeButtons(QPalette::Active, KColorScheme::Button);
 	const QColor defaultColor = schemeButtons.background().color();
 
@@ -2178,7 +2183,8 @@ void KCalculator::setColors() {
 			&& KCalcSettings::statButtonsColor()      == defaultColor
 			&& KCalcSettings::hexButtonsColor()       == defaultColor
 			&& KCalcSettings::memoryButtonsColor()    == defaultColor
-			&& KCalcSettings::operationButtonsColor() == defaultColor) {
+			&& KCalcSettings::operationButtonsColor() == defaultColor
+			&& KCalcSettings::constantsButtonsColor() == defaultColor) {
 		return;
 	}
 
@@ -2213,6 +2219,11 @@ void KCalculator::setColors() {
 	foreach(QAbstractButton *btn, operation_button_list_) {
 		btn->setStyleSheet(sheet.arg(opPal.name()));
 	}
+
+	const QColor coPal(KCalcSettings::constantsButtonsColor());
+	foreach(QAbstractButton *btn, const_buttons_) {
+		btn->setStyleSheet(sheet.arg(coPal.name()));
+	}
 }
 
 //------------------------------------------------------------------------------

kcalc.kcfg

@@ -45,6 +45,10 @@
       <label>The color of operation buttons.</label>
       <default code="true">defaultButtonColor</default>
     </entry>
+    <entry name="ConstantsButtonsColor" type="Color">
+      <label>The color of constants buttons.</label>
+      <default code="true">defaultButtonColor</default>
+    </entry>
     <entry name="NumberFontsColor" type="Color">
       <label>The color of number fonts.</label>
       <code>KColorScheme schemeFonts(QPalette::Active, KColorScheme::Button);
@@ -71,6 +75,10 @@
       <label>The color of operation font.</label>
       <default code="true">defaultFontColor</default>
     </entry>
+    <entry name="ConstantsFontsColor" type="Color">
+      <label>The color of constants fonts.</label>
+      <default code="true">defaultFontColor</default>
+    </entry>
   </group>
   <group name="Font">
     <entry name="ButtonFont" type="Font">

kcalc_const_button.cpp

@@ -35,6 +35,7 @@ along with this program.  If not, see <http://www.gnu.org/licenses/>.
 //------------------------------------------------------------------------------
 KCalcConstButton::KCalcConstButton(QWidget *parent) : KCalcButton(parent), button_num_(-1) {
 
+	setTextColor(KCalcSettings::constantsFontsColor());
 	addMode(ModeShift, i18nc("Write display data into memory", "Store"), i18n("Write display data into memory"));
 	initPopupMenu();
 	connect(this, &QAbstractButton::clicked, this, &KCalcConstButton::slotClicked);
@@ -46,6 +47,7 @@ KCalcConstButton::KCalcConstButton(QWidget *parent) : KCalcButton(parent), butto
 //------------------------------------------------------------------------------
 KCalcConstButton::KCalcConstButton(const QString &label, QWidget *parent, const QString &tooltip) : KCalcButton(label, parent, tooltip), button_num_(-1) {
 
+	setTextColor(KCalcSettings::constantsFontsColor());
 	addMode(ModeShift, i18nc("Write display data into memory", "Store"), i18n("Write display data into memory"));
 	initPopupMenu();
 }