"В общем что нужно для начала. Основные цвета фронта и какой основной шрифт."

У нас более 200 цветов, так что лучше по требованию отсылать.
Вот дефолтные для окон:

<!-- Default Windows -->
    <SolidColorBrush x:Key="defaultWindowBg" Color="#FF3F4140"/>
    <SolidColorBrush x:Key="defaultPopupBg" Color="Gainsboro"/>
    <Color x:Key="defaultFooterColor">#FF202020</Color>
    <SolidColorBrush x:Key="loyaltyActionNameBg" Color="#FF202020"/>
    <SolidColorBrush x:Key="defaultFooterBg" Color="#FF202020"/>
    <SolidColorBrush x:Key="defaultHeaderBg" Color="#FFFEFEFE"/>
    <SolidColorBrush x:Key="cashPageBg" Color="#FFB6B6B8"/>
    <SolidColorBrush x:Key="waiterBg" Color="#FFE9E9E9"/>
    <SolidColorBrush x:Key="attendenceBg" Color="#FF676767"/>

    <SolidColorBrush x:Key="defaultColorLightGrey" Color="#FFDADADC"/>
    <SolidColorBrush x:Key="defaultColorGrey" Color="#FFA0A0A0"/>
    <SolidColorBrush x:Key="defaultColorDarkGrey" Color="#FF555555"/>
    <SolidColorBrush x:Key="defaultColorBlack" Color="#FF303030"/>
    <SolidColorBrush x:Key="defaultColorRed" Color="#FF9B1D21"/>
    <SolidColorBrush x:Key="defaultColorLightGreen" Color="#FF94F3A5"/>

Шрифты:
    <FontFamily x:Key="default_FontFamily">Segoe UI Light</FontFamily>

    <FontFamily x:Key="semibold_FontFamily">Segue UI Semilight</FontFamily>
    <FontFamily x:Key="bold_FontFamily">Segoe UI Regular</FontFamily>
    <FontFamily x:Key="bolder_FontFamily">Segoe UI SemiBold</FontFamily>
    <FontFamily x:Key="extrabold_FontFamily">Segoe UI Bold</FontFamily>
    <FontFamily x:Key="default_MonospaceFontFamily">Courier New</FontFamily>

	

"С главного экрана хочется контрол Назад (они у вас кстати через изображения или векторно нарисованы?)"
Стиль кноки с зависимостями слишком большой  - вынес в отдельный файл:
ToggleButton - GeneralToggleTextButtonStyle
Кнопка назад - BackButtonStyle
Кнопка в шапке с иконкой - TopIconButtonBase


Все изображения во фронте векторные.

Блокировка экрана:
<PathGeometry x:Key="LockIcon"
                  Figures="M 489.843,349.395 M 489.843,349.395 L 175.202,349.395 L 175.202,270.489 C 175.202,183.563 245.775,111.691 332.476,111.691 C 419.183,111.691 489.843,183.563 489.843,270.489 L 489.843,349.395 Z M 385.937,606.751 L 385.937,726.346 C 385.937,740.033 374.466,751.619 360.796,751.619 L 304.157,751.619 C 290.493,751.619 279.068,740.033 279.068,726.346 L 279.068,606.751 C 265.803,593.692 258.008,575.587 258.008,555.582 C 258.008,517.650 287.355,485.077 324.594,483.577 C 328.536,483.416 336.464,483.416 340.410,483.577 C 377.644,485.077 406.997,517.650 406.997,555.582 C 406.997,575.587 399.243,593.692 385.937,606.751 L 385.937,606.751 Z M 617.771,349.395 L 600.968,349.395 L 600.968,270.489 C 600.968,124.570 485.186,2.649 340.410,0.052 C 336.464,-0.017 328.536,-0.017 324.594,0.052 C 179.817,2.649 64.030,124.570 64.030,270.489 L 64.030,349.395 L 47.141,349.395 C 21.239,349.395 0.000,376.191 0.000,409.305 L 0.000,805.027 C 0.000,838.096 21.239,865.162 47.141,865.162 L 617.771,865.162 C 643.805,865.162 665.000,838.096 665.000,805.027 L 665.000,409.305 C 665.000,376.191 643.805,349.395 617.771,349.395 L 617.771,349.395 Z"/>
    <PathGeometry x:Key="UnlockIcon"
                  Figures="M 104.332,199.979 L 104.332,232.309 C 104.332,236.009 101.231,239.141 97.536,239.141 L 82.224,239.141 C 78.530,239.141 75.442,236.009 75.442,232.309 L 75.442,199.979 C 71.855,196.449 69.748,191.554 69.748,186.146 C 69.748,175.892 77.682,167.086 87.749,166.681 C 88.815,166.637 90.958,166.637 92.024,166.681 C 102.090,167.086 110.026,175.892 110.026,186.146 C 110.026,191.554 107.929,196.449 104.332,199.979 Z M 168.417,130.588 L 47.363,130.588 L 47.363,73.122 C 47.363,49.623 66.441,30.193 89.880,30.193 C 113.320,30.193 132.421,49.623 132.421,73.122 L 132.421,94.322 L 162.463,94.322 L 162.463,73.122 C 162.463,33.675 131.163,0.716 92.024,0.014 C 90.958,-0.005 88.815,-0.005 87.749,0.014 C 48.611,0.716 17.310,33.675 17.310,73.122 L 17.310,130.588 L 11.338,130.588 C 4.998,131.490 0.000,138.266 0.000,146.603 L 0.000,253.580 C 0.000,262.519 5.743,269.836 12.744,269.836 L 167.005,269.836 C 174.043,269.836 179.773,262.519 179.773,253.580 L 179.773,146.603 C 179.773,138.266 174.784,131.490 168.417,130.588 Z"/>


Изображение стрелка (назад):
<PathGeometry x:Key="LeftArrowSymbol"
                  Figures="M 20.457,450.519 M 20.457,450.519 L 450.510,20.508 C 477.893,-6.836 522.244,-6.836 549.589,20.508 C 576.848,47.848 576.848,92.204 549.589,119.544 L 169.118,500.015 L 549.504,880.444 C 576.848,907.788 576.848,952.098 549.504,979.399 C 522.164,1006.867 477.850,1006.867 450.510,979.399 L 20.457,549.474 C 6.849,535.781 0.000,517.898 0.000,500.015 C 0.000,482.090 6.849,464.085 20.457,450.519 L 20.457,450.519 Z"/>
				 


Иконка гамбургер (3 полоски):
<PathGeometry x:Key="AdditionalMenuIcon"
                  Figures="M23.896994,558.125 L716.24799,558.125 C729.448,558.125 740.14801,568.86297 740.14801,582.026 L740.14801,688.341 C740.14801,701.52197 729.448,712.276 716.24799,712.276 L23.896994,712.276 C10.734,712.276 0,701.52197 0,688.341 L0,582.026 C0,568.86297 10.734,558.125 23.896994,558.125 z M23.896994,279.07199 L716.24799,279.07199 C729.448,279.07199 740.14801,289.806 740.14801,302.95401 L740.14801,409.26901 C740.14801,422.46899 729.448,433.22198 716.24799,433.22198 L23.896994,433.22198 C10.734,433.22198 0,422.46899 0,409.26901 L0,302.95401 C0,289.806 10.734,279.07199 23.896994,279.07199 z M23.896994,4.5474735E-13 L716.24799,4.5474735E-13 C729.448,-2.7149435E-06 740.14801,10.733997 740.14801,23.896995 L740.14801,130.216 C740.14801,143.416 729.448,154.169 716.24799,154.169 L23.896994,154.169 C10.734,154.169 0,143.416 0,130.216 L0,23.896995 C0,10.733997 10.734,-2.7149435E-06 23.896994,4.5474735E-13 z"/>