Make default avatar colors less aggressive

iOS does not set a color by default.

src/threema/container.ts

@@ -140,7 +140,7 @@ class Receivers implements threema.Container.Receivers {
     public setContacts(data: threema.ContactReceiver[]): void {
         this.contacts = new Map(data.map((c) => {
             c.type = 'contact';
-            setDefault(c, 'color', '#ff00ff');
+            setDefault(c, 'color', '#f0f0f0');
             return [c.id, c];
         }) as any) as ContactMap;
         if (this.me !== undefined) {
@@ -236,7 +236,7 @@ class Receivers implements threema.Container.Receivers {
         let contactReceiver = this.contacts.get(data.id);
         if (contactReceiver === undefined) {
             data.type = 'contact';
-            setDefault(data, 'color', '#ff00ff');
+            setDefault(data, 'color', '#f0f0f0');
             this.contacts.set(data.id, data);
             return data;
         }